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
a) made trap_exception work
b) updated manual and examples to show how to use library to eliminate runtime penalty
c) added in safe_literal
d) made corrections of various types
