Valijson v0.5

This is mostly a maintenance release. It addresses a number of warnings that were produced when compiling with warnings enabled (/W4) on MSVC. In some cases, warnings have been suppressed on a per-file basis, through the use of pragma statements. This was done to minimise the potential impact of changes required to exhaustively address these warnings.

Bundled versions of gtest and rapidjson have also been updated, and several minor bug fixes have been included.