Log Message:
Update to 0.5.1
Update LICENSE

Upstream changes:
        CHANGES IN highr VERSION 0.5

MAJOR CHANGES

  o the minimal required R version is 3.0.2 now

        CHANGES IN highr VERSION 0.4

BUG FIXES

  o hi_andre() may fail to find highlight under OS X (thanks, Christopher
  Gandrud, #2)

MINOR CHANGES

  o :: and ::: are recognized as operators, and they will be syntax highlighted
  in the same way as other operators like +, -, *, and /, etc (thanks, Qiang Li)