removed singularity, introduced global_context and updated tests
added tests for global_context
now using boost_throw_exception in global_context
updated examples to use global_context
updated self-pipe example to global_context
updating examples, docs, etc to global_context complete now
changed mutex to shared_lock as global_context::get() does not need exclusive locking
Merge branch 'feature/remove_singularity'
fixed merge
Merge branch 'master' of https://github.com/retf/Boost.Application