removed constexpr from exception policies.
this eliminates obstacle to gcc compilation which doesn't support constexpr throw
unfortunately, all versions of gcc trip compiler fault so gcc not supported for now
safe_literal - make this an unsafe type since it doesn't have policies - this might change in the future
passes all tests
adds documentation of library internals
implements trap_exception for compile time guarantee for program correctness
still needs update to support the above for operations in addition to + and -
This lead to numerous small changes - which of course weren't so small
Added static asserts for some range construction / assignments.
Passing all tests.
