Remove redundant specs

`expect_twins` already checks both directions, so no need to repeat examples with reversed arguments.
Fix “Alternate File” for /app/lib/foobar.rb

Fixes #64
Add file for manually checking syntax highlighting

Currently there is no good to automate tests for the syntax highglighting.  But this is better than nothing.
Fix #45
Fix #31
Merge remote-tracking branch 'upstream/master'