add change handling for props

[andyrichardson]

• Updates event handlers on prop change
• Removes switch logic for lookup map
• Removes event handlers on unmount

Fix #142

[coveralls]

Coverage increased (+15.9%) to 97.059% when pulling c28117d2662da614b3808692f2f59da31a2d3ef9 on andyrichardson:fix-prop-change-handler into a633e7dd673ddf5bdb07e2ed664a03aa47159bfa on scniro:master.

[scniro]

@andyrichardson I am a lot shorter on time these days as when I started this project. Codemirror & React APIs are moving to quickly for me to keep atop of for the day-to-day. I am looking for a co-maintainer of this project. Please contact me directly if you are interested. Thank you for understanding.