make History.md non-executable
consistenly use double quotes in Appraisals
stub is deprecated. Use double instead.
alphabetize dependencies
update yard dependency

No reason to lock to ~> 0.8.5.2.
update rdoc dependency

No reason to lock to ~> 3.12.2.
update rdiscount dependency

No reason to lock to ~> 2.0.7.
Merge pull request #264 from sferik/cleanup

Various bundler-related fixes