MSVS Tools 0.7.0

• Various shellcheck overhauls and other hardening (#16, @dra27)
• Preview versions of Visual Studio are now included in results (#17, @dra27)
• New options --installed and --output=data (#17, @dra27)
• Various fixes to environment compiler detection and results (#17, @dra27)
• opam packaging for msvs-detect exposed as conf-msvc32 and conf-msvc64 packages (#18, @dra27)