Preprocessor defines for serialization function names

The following preprocessor defines have been added:

 - CEREAL_SERIALIZE_FUNCTION_NAME
 - CEREAL_SAVE_FUNCTION_NAME
 - CEREAL_LOAD_FUNCTION_NAME

These defines specifiy the name of the cereal serialization/deserialization
functions so that they can be customised by users. This is especially useful if
the user would like to have capitialized function names.
Merge branch 'capitalization' of https://github.com/mattyclarkson/cereal into mattyclarkson-capitalization

Conflicts:
	include/cereal/types/common.hpp
Adding macros for minimal functions

Also added some documentation to macros.hpp

relates #60
Merge branch 'mattyclarkson-capitalization' into develop