Backported to VS2013 using a metaprogrammed emulation of unrestricted unions.
Typo fix.
Silly wrong GCC version detect.
Bad constexpr overload.
Removed unnecessary template declaration.

Replaced error_exception with explicit construction for VS2013.
Figured out a workaround for functor map() not compiling on VS2013.
Merge branch 'master' of https://github.com/ptal/Boost.Expected
Fixed up Readme.
Merge branch 'master' of github.com:ned14/Boost.Expected
Merge pull request #70 from ned14/master

Backported to VS2013 using a metaprogrammed emulation of unrestricted unions. Works surprisingly well considering.