fixed small typos
added 'pragma once' to generated header files
generate SA-MP natives in 'sampgdk' namespace
Refactoring and coding style fixes
Fix compile errors in helloworld
Replace '#pragma once' with incldue guard
Make C++ wrappers optional

Make it possible to enable/disable C++ wrappers around SA-MP natives
via defining/undefining SAMPGDK_CPP_WRAPPERS. By default it is not
defined (for backwards compatibility).
Add default arguments for C++ native wrappers