Python: Added support for file_identifiers (#5123)

* Python: Added support for file_identifiers

* Added tests. Fixed file_identifier code.

* Python: Fixed excessive padding of file_identifier. Repaired tests.

* Python: Made code compatible with python2.7

* Python: Typo fix in @endcond

* whitespace normaalization

* Stylistic change from if(not X is None) to if(X is not None). Added comment to type string.

* Python: Added support for automatic code generation of file_identifiers. Added tests for said code generation.

* converted sprintf to snprintf

* Bugfix, added snprint deffinition for MSVC

* changed snprint deffinition for MSVC to sprint_s

* changed scanf to IntToStringHex. Renamed HasFileIdentifier to GenHasFileIdentifier.

* Added updated genereated code to commit

* Python bugix: flatc no longer produces HasFileIdentfier for shcemas with no file identifier

* Added tests to verify `MonsterBufferHasIdentifier` returns false on no Identifier

* Python: added tests for GetBufferIdentifier and BufferHasIdentifier
Python: removed unessasary parenethesis in if statements
Minor format changes.

* Python : correceted instances of keyword arguments being called as positional arguments

* fixed typos and grammer in comments

* Minor style fixes

* Indentation fix

* Equals style changes

* Python: Fixed Alignment Issues. Changed test code to test against atual output

* Ran make(forgot to run make last commit)

* Python: Style changes

* Style changes

* indentation and style

* readded CONTRIBUTING.md

* Formatting tweak

Mostly to make CI run again

* More formatting fixes

* More formatting fixes

* More formatting fixes

* More formatting fixes

* Formatting fix

* More formatting fixes

* Formatting

* ran generate_code.sh

python/flatbuffers/encode.py

@@ -19,6 +19,8 @@ from .compat import import_numpy, NumpyRequiredForThisFeature
 
 np = import_numpy()
 
+FILE_IDENTIFIER_LENGTH=4
+
 def Get(packer_type, buf, head):
     """ Get decodes a value at buf[head] using `packer_type`. """
     return packer_type.unpack_from(memoryview_type(buf), head)[0]