Add some more styling options

- Add method for setting the typeface.
- Remove the title's top margin so that users can have less whitespace above the calendar if they want. Instead add a nonzero default separation.
- Add option to hide the header row with week abbreviations. In our case we'd like a global header row, not one for each month.
this seems bad...if you don't want any topmargin on the month cells, couldn't your app just override this value to 0?