Option post date format

[adampatterson]

Allow a user to submit a post date format.

 *   F j, Y g:i a - November 6, 2010 12:50 am
 *   F j, Y - November 6, 2010
 *   F, Y - November, 2010
 *   g:i a - 12:50 am
 *   g:i:s a - 12:50:48 am
 *   l, F jS, Y - Saturday, November 6th, 2010
 *   M j, Y @ G:i - Nov 6, 2010 @ 0:50
 *   Y/m/d \a\t g:i A - 2010/11/06 at 12:50 AM
 *   Y/m/d \a\t g:ia - 2010/11/06 at 12:50am
 *   Y/m/d g:i:s A - 2010/11/06 12:50:48 AM
 *   Y/m/d - 2010/11/06