Python flatbuffers read support

Python code generator for flatbuffers reading.
Just a small thing, we follow the Google C++ style guide
http://google-styleguide.googlecode.com/svn/trunk/cppguide.html

To adhere to this, you'll need to line up the arguments followed by the function definition to the opening parenthesis:

e.g

+extern bool GeneratePython(const Parser &parser,
+                           const std::string &path,
+                           const std::string &file_name,
+                           const GeneratorOptions &opts);