Add adjustable arrow barb location
Merge branch 'master' into enh/barb-location

Conflicts:
	frontend/js/vector.js
Cleanup barb placement logic
Fix bug preventing tail placement
Merge branch 'master' into enh/barb-location

Conflicts:
	frontend/js/vector.js
Merge pull request #24 from enthought/enh/barb-location

Add adjustable arrow barb location