Merge pull request #49 from glynos/master

Added clear member functions  to uri_builder
Merge pull request #51 from glynos/master

Allow a forward slash to be prefixed for paths that don't have them in the builder
Added some extra tests for the scheme; removed some incorrect tests.
Fixed up resolve tests.
Fixed encoding tests.
Given up hope of compiling MSVC 2013, so I'm removing the macros.
Fixed failing builds due to removals in previous commit.
Fixed tests so that they compile for Boost.Optional in 1.56.
Removed tests that are actually expected to fail.