Add Option To Remove Year from Table Header H2

For your consideration: 
 I have a project I'm using this on and was removing the year display in the header with Javascript and thought this might be a better option. I added a simple option to include dont_display_year set to true to only show the month as I'm using this sweet gem to show all the months for the calendar year. 

I also updated one of your tests to check the header for the full text that is display and removed your to-do. Please let me know if this is overstepping my bounds or not implemented how you planned and I will revert

Example: 
http://cl.ly/image/2v0a0U0t1Q3h

Thanks for your time and for writing this! Very helpful.