(maint) Use 7za instead of modifying PATH

The 7zip.commandline package installs a script 7za that calls 7z. Use
this instead of hard-coding the path to 7-Zip by adding it to PATH.
Merge pull request #155 from MikaelSmith/maint/master/use-7za

(maint) Use 7za instead of modifying PATH
(maint) Use ctest -V on Windows

This makes it easier to debug when unit tests fail. It follows the
redirection and filtering used for Travis runs.
(maint) Fix Ruby version to 2.0.0