Devel bounds (#60)

* refactor: Use 'args' property instead of '_args' attribute.

As described in Sympy's User Guide, one should never use internal
methods of variables, prefixed with '_' (as an example, it is explicitly
written that one should not use '_args', but use 'args' instead).

Here we apply this rule to the two main modules in the 'topology'
directory: 'basic' and 'domain'.

* refactor: Improve Boundary class

* refactor: Remove obsolete module

* feat: Add coord bounds to Line/Square/Cube domains

Several changes in 'domain' module:

* It is now possible to instantiate objects of type Line, Square and
  Cube (these classes were only used as Domain constructors before);

* Line, Square and Cube are subclasses of the generic NCube class, they
  have different constructor signatures, and use NCube's constructor to
  instantiate an object of their type with minimal code duplication;

* NCube is a subclass of Domain; its constructor returns a Line object
  for dim=1, a Square for dim=2, a Cube for dim=3, and a generic NCube
  for dim>=4;

* Line, Square, Cube, and NCube allow the user to prescribe the
  coordinate bounds, which are (0, 1) by default.

Moreover, unit tests for the new features are provided.

* chore: Do not use latest version of Sympy (1.5)

* refactor: Avoid Codacy errors

setup.py

@@ -38,7 +38,7 @@
 
 # Dependencies
 install_requires = [
-    'sympy>=1.2',
+    'sympy>=1.2,<1.5',
     'h5py',
     'pytest',
     'pyyaml',

sympde/topology/basic.py

@@ -62,7 +62,7 @@ def __new__(cls, name, dim=None):
 
     @property
     def name(self):
-        return self._args[0]
+        return self.args[0]
 
     @property
     def target(self):
@@ -122,31 +122,31 @@ def __new__(cls, *args):
 
     @property
     def dim(self):
-        return self._args[0].dim
+        return self.args[0].dim
 
     def __len__(self):
-        return len(self._args)
+        return len(self.args)
 
     def complement(self, arg):
         if isinstance(arg, Union):
-            arg = arg._args
+            arg = arg.args
         elif isinstance(arg, BasicDomain):
             arg = [arg]
         elif arg is None:
             return self
         else:
             TypeError('Invalid argument {}'.format(arg))
 
-        return Union(*[i for i in self._args if (i not in arg)])
+        return Union(*[i for i in self.args if (i not in arg)])
 
     def __sub__(self, other):
         return self.complement(other)
 
     def todict(self):
-        return [i.todict() for i in self._args]
+        return [i.todict() for i in self.args]
 
     def as_tuple(self):
-        ls = [i for i in self._args]
+        ls = [i for i in self.args]
         return tuple(ls)
 
 #==============================================================================
@@ -161,11 +161,12 @@ def __new__(cls, *args, name=None):
         obj = Basic.__new__(cls, *args)
         obj._dim = sum(i.dim for i in args)
         obj._name = name
+
         return obj
 
     @property
     def domains(self):
-        return self._args
+        return self.args
 
 #==============================================================================
 class Interval(InteriorDomain):
@@ -193,7 +194,7 @@ def __new__(cls, name=None, coordinate=None, bounds=None):
 
     @property
     def name(self):
-        return self._args[0]
+        return self.args[0]
 
     @property
     def bounds(self):
@@ -209,37 +210,35 @@ class Boundary(BasicDomain):
     """
     def __new__(cls, name, domain, axis=None, ext=None):
 
-        if not( axis is None ):
-            assert(isinstance(axis, int))
+        if axis is not None:
+            assert isinstance(axis, int)
 
-        if not( ext is None ):
-            assert(isinstance(ext, int))
+        if ext is not None:
+            assert isinstance(ext, int)
+
+        obj = Basic.__new__(cls, name, domain, axis, ext)
 
-        obj = Basic.__new__(cls, name)
-        obj._domain = domain
-        obj._axis = axis
-        obj._ext = ext
         return obj
 
     @property
     def name(self):
-        return self._args[0]
+        return self.args[0]
 
     @property
     def domain(self):
-        return self._domain
-
-    @property
-    def dim(self):
-        return self.domain.dim
+        return self.args[1]
 
     @property
     def axis(self):
-        return self._axis
+        return self.args[2]
 
     @property
     def ext(self):
-        return self._ext
+        return self.args[3]
+
+    @property
+    def dim(self):
+        return self.domain.dim
 
     def _sympystr(self, printer):
         sstr = printer.doprint
@@ -264,19 +263,6 @@ def todict(self):
 
         return OrderedDict(sorted(d.items()))
 
-    def __hash__(self):
-        return hash(self.name)
-
-    def __lt__(self, other):
-        #add this method to avoid sympy error in Basic.compare
-        return 0
-
-    def __eq__(self, other):
-        if not isinstance(other, Boundary):
-            return False
-
-        return ( self.name == other.name ) and ( self.domain is other.domain )
-
 #==============================================================================
 class Interface(BasicDomain):
     """
@@ -303,15 +289,15 @@ def dim(self):
 
     @property
     def name(self):
-        return self._args[0]
+        return self.args[0]
 
     @property
     def minus(self):
-        return self._args[1]
+        return self.args[1]
 
     @property
     def plus(self):
-        return self._args[2]
+        return self.args[2]
 
     def _sympystr(self, printer):
         sstr = printer.doprint