Add useful options to surface information to end user

[rkstar]

• getCurrentPage() returns the currently active page index
• updatePagesInBuffer allows user to specify how many pages on either side of active component should re-render when active changes
• isAdjacentToActive allows user to know if a buffer page is adjacent to the active page

[ryskin]

updatePagesInBuffer - that really good idea, yesterday I had it in mind.

when I'm at the first date on the calendar I'm able to move right once and 6 times to the right. So I don't need 6 screens from left and 6 from right.