Further additions of BOOST_ prefix to macros

The focus for this commit was mainly on triplegit.hpp and async_io.hpp

TODO:
There is some issue changing TRIPLEGIT_DLL_EXPORTS in async_file_io.hpp
a dependency or another instance of this exists outside of the 4 files
comprising the heart of AFIO lib

I'll need some time to work this out, but few macros exist in the main lib

Future tasks:
1. convert TRIPLEGIT_DLL_EXPORTS to BOOST_AFIO_DLL_EXPORTS, and not break the codebase
2. track down any missed macros
3. convert file names and directory structure to Boost ready
4. convert CHECK to BOOST_TEST with preprocessor directives