Handle preprocessor_path == ""

When using the asset pipepline, the font-url helper need to receive the name of the font width a slash in the beginning to properly compile assets.

This modifications adds a new ternary to handle the case where preprocessor_path is "" and don't put a slash with the name.
Adds realdirpath to make output paths more robust
Beta version bump
Fixes bug where preprocessor_path is ignored by scss template
Adds spec sandbox to gitignore
Update travis ruby versions
Updates travis versions again
Merge branch 'patch-1' of https://github.com/wlepinski/fontcustom into wlepinski-patch-1
Expands double ternary
Allow preprocessor_path: false, fixes specs
Update docs, version bump
Merge remote-tracking branch 'upstream/master' into moar_font_metrics

* upstream/master:
  Update docs, version bump
  Allow preprocessor_path: false, fixes specs
  Expands double ternary
  Updates travis versions again
  Update travis ruby versions
  Adds spec sandbox to gitignore
  Fixes bug where preprocessor_path is ignored by scss template
  Beta version bump
  Adds realdirpath to make output paths more robust
  Handle preprocessor_path == ""