Changed TRIPLEGIT_DLL_EXPORT to BOOST_AFIO_DLL_EXPORT

This change required an alteration to the SConscript file

Some additionall changes of macros to use BOOST_prefix as well.

One or two more commits to complete this task

TODO:
1. Finish last conversion of macros to use BOOST_prefix
2. Change CATCH to use BOOST_TEST with preprocessor directives
3. restructure file hierarchy and file names
4. refactor NiallsCPPUtilities into details folder
5. change build commands as needed to keep using scons
6. convert from scons to BOOST.Build