Enhance araxis-merge cask to link command line utilities

[RogerThiede]

http://www.araxis.com/merge/documentation-os-x/installing.en recommends optional instructions to install the merge command line utilities:

Ensure that the Utilities folder within the Araxis Merge application bundle is part of your command-line shell’s search path.

~/Applications/Araxis Merge.app/Contents/Utilities/

• araxisgitdiff
• araxisgitmerge
• araxishgmerge
• araxisopendiff
• araxisp4diff
• araxisp4winmrg
• araxissvndiff
• araxissvndiff3
• araxissvnmerge
• compare
• compare2

Instead of modifying the user's PATH environment variable, enhance the araxis-merge cask to create sym-links for each command line utility in $(brew --prefix)/bin pointing to the Araxis Merge application bundle path. Curiously, the application bundle path may have been modified such as with HOMEBREW_CASK_OPTS="--appdir=/Applications"

I believe the cask binary stanza would suffice for this:
binary 'Araxis Merge.app/Contents/Utilities/araxisgitdiff', :target => 'araxisgitdiff'

[tapeinosyne]

Symlinks added in 065a5ec. Thanks.