add: python3 support + default formatting rules

[YYYasin19]

Hi,

not sure whether this can be helpful for anyone in the future, but I've updated some of the lines to be compatible with Python3. The functionality should be unchanged.

Thanks for making this!

[EpicOrange]

Thanks for doing this! I also had to update these lines:

gpt-surgeon/gpt_surgeon.py

Lines 83 to 85 in 12fc326

	rawHeader = struct.pack(efiHeaderFmt,
	efiSignature, efiExpectedVersion,
	efiHeaderExpectedSize, 0,

==>

 	 rawHeader = struct.pack(efiHeaderFmt.format('utf-8'), 
	                         efiSignature.format('utf-8'), efiExpectedVersion.format('utf-8'), 
	                         efiHeaderExpectedSize, 0, 

and

gpt-surgeon/gpt_surgeon.py

Line 184 in 12fc326

disk.write("\x00" * (blockSize - len(header)))

==>

 	 disk.write(b"\x00" * (blockSize - len(header)))