[#26] Fix: app does not render stanza names if bars are reused.
[#26] As a developer, I want the option to run the app specs with lilypond enabled.
  The app specs should tell if lilypond was able to generate the pdfs and midis.
  The app specs should not delete the pdfs so that I can inspect them manually.
[#26] Fix examples: lilypond 2.14 doesn't like #'(4 -1 -5 -10 -15 -22). Use #guitar-drop-d-tuning instead.
[#26] UNSTABLE. Fix: Stanza#heading_in_lilypond doesn't compute bar lengths correctly.
  Broke: Bar#stanza doesn't seem to pick up stanza if bar is a reused bar.
[#26] Fix: Bar#stanza cannot find the stanza if the stanza's bar is defined outside the stanza.
  Solution: Let Stanza handle #heading_for_first_bar instead of Bar#stanza_heading_for_first_bar.
[#26] Update app_spec: test all rb files in examples.
  Move complete tab examples to examples directory.
  Add midis and pdfs to examples directory.
[#26] Remove stanza versions of bars and lines from generated lilypond.
  Update tab.erb: stanzaHeadings should be blank if there are no stanzas.