Add cached format functions for 3x faster formatting.

[timrwood]

Not ready to pull in, opening discussion.

TODO: inline L LL LLL LLLL LT tokens.

Some speed tests:

http://jsperf.com/date-formatting/8
http://jsperf.com/momentjs-cached-format-functions

All make test-moment tests are passing now, need to add support for L LL LLL LLLL LT for all tests to pass.

File size difference
-108b minified
+75b gzipped

Though there are probably some byte squeezing techniques we could add.

[timrwood]

Also, we can probably do something similar with the parser.

[bankyadam]

You can save 1 byte by using /(LT|L{1,4})/g

[dmitriy-kiriyenko]

I also believe that /L{1,4}/ works faster then /LL?L?L?/.

And same pattern used in the line above. I'd say, abused =)

[timrwood]

Performance looks about the same between /(LT|L{1,4})/g and /(LT|LL?L?L?)/g. The saved byte is good though!

http://jsperf.com/regex-optional-vs-length

[timrwood]

For exposing formatting tokens, I was thinking of using this syntax.

moment.formatToken('MM', 'p(t.month()+1,2)'); // set a format token
moment.formatToken('MM'); // 'p(t.month()+1,2)' (get a format token)

Alternatively, we could use token, but that might be insufficiently named as parsing tokens are not affected. I don't plan on exposing parsing tokens (and it would be difficult with the incremental parser) but we may need to in the future...

moment.token('MM', 'p(t.month()+1,2)'); // set a format token
moment.token('MM'); // 'p(t.month()+1,2)' (get a format token)

[rockymeza]

I think that the cached formatters should go out in 1.7, but if we ever do do extensible formatting that should not. The 3x boost for 1.7 seems to be ready already