a:am/pm
a:0~86399999 (millisecond of day)
C/cc:1~7 (Day of Week)
Ccc:sun/mon/tue/wed/thu/fri/sat
Cccc:sunday/monday/tuesday/wednesday/thursday/friday/saturday
D:1~31 (0 padded day of Month)
d:1~366 (0 padded day of the year)
E:1~7 (0 padded day of Week)
E~eee:sun/mon/tue/wed/thu/fri/sat
Eeee:sunday/monday/tuesday/wednesday/thursday/friday/saturday
F:1~5 (0 padded Week of Month, day of Week = Monday)
G:julian Day number (number of days since 4713 BC January 1)
G~ggg:bc/ad (Era designator abbreviated)
Gggg:before Christ/anno Domini
H:1~12 (0 padded Hour (12hr))
h:0~23 (0 padded Hour (24hr))
K:1~24 (0 padded Hour (24hr)
K:0~11 (0 padded Hour (12hr))
L/LL:1~12 (0 padded Month)
Lll:jan/feb/mar/apr/may/jun/jul/aug/sep/oct/nov/dec
Llll:january/february/march/april/may/june/july/august/september/october/november/december
m:0~59 (0 padded Minute)
M/MM:1~12 (0 padded Month)
Mmm:jan/feb/mar/apr/may/jun/jul/aug/sep/oct/nov/dec
Mmmm:january/february/march/april/may/june/july/august/september/october/november/december
Q/qq:1~4 (0 padded quarter)
Qqq:q1/q2/q3/q4
qqqq:1st quarter/2nd quarter/3rd quarter/4th Quarter
Q/qq:1~4 (0 padded quarter)
Qqq:q1/q2/q3/q4
qqqq:1st quarter/2nd quarter/3rd quarter/4th Quarter
s:0~59 (0 padded Second)
S: (Rounded sub-second)
U: (0 padded year)
V~VVV: (General GMT Timezone abbreviation)
VVVV: (General GMT Timezone Name)
w:1~53 (0 padded Week of year, 1st/Week = Sunday, nb:1st Week of year starts to last Sunday
W:1~5 (0 padded Week of Month, 1st day of Week = Sunday)
Y/YYYY: (Full year)
YY/YYY: (2 Digits year)
Y/YYYY: (starting from the Sunday of the 1st week of year)
YY/YYY: (2 Digits year, starting from the Sunday of the 1st week of year)
Z~ZZZ: (Specific GMT Timezone abbreviation)
ZZZZ: (Specific GMT Timezone Name)
Z: +0000 (RFC 822 Timezone)
Turn from: http://www.alexcurylo.com/blog/2009/01/29/nsdateformatter-formatting/
