Copied from: http://exploded.awcr.org/DrupalDate
* a - am or pm
* A - AM or PM
* d - day of the month, 2 digits with leading zeros; i.e. 01 to 31
* D - day of the week, textual, 3 letters; i.e. Fri
* F - month, textual, long; i.e. January
* h - hour, 12-hour format; i.e. 01 to 12
* H - hour, 24-hour format; i.e. 00 to 23
* g - hour, 12-hour format without leading zeros; i.e. 1 to 12
* G - hour, 24-hour format without leading zeros; i.e. 0 to 23
* i - minutes; i.e. 00 to 59
* j - day of the month without leading zeros; i.e. 1 to 31
* l (lowercase 'L') - day of the week, textual, long; i.e. Friday
* L - boolean for whether it is a leap year; i.e. 0 or 1
* m - month; i.e. 01 to 12
* n - month without leading zeros; i.e. 1 to 12
* M - month, textual, 3 letters; i.e. Jan
* s - seconds; i.e. 00 to 59
* S - English ordinal suffix, textual, 2 characters; i.e. th, nd
* t - number of days in the given month; i.e. 28 to 31
* U - seconds since the epoch
* w - day of the week, numeric, i.e. 0 (Sunday) to 6 (Saturday)
* Y - year, 4 digits; i.e. 1999
* y - year, 2 digits; i.e. 99
* z - day of the year; i.e. 0 to 365
* Z - timezone offset in seconds (i.e. -43200 to 43200)