Remove Camlp4 and only support PPX, support OCaml 4.03

avsm released this 27 Apr 14:34

daafda7

Remove camlp4 extension as it is no longer maintained (#95).
Add support for OCaml 4.03 in the PPX extension (#96).
Minimum supported OCaml version for the library is now 4.02.3.
Fix parsing of high int32 @@enum values.

Assets 2