Add ability to limit characters in text and textarea fields

[dannycolin]

Issue description:

I can't limit the number of character in a text or textarea fields. It would be great to have it builtin with a counter like on twitter for example.

Version used:

v3.0.33

Using theme_mods or options?

theme_mods

Code to reproduce the issue (config + field(s))

Do not apply. it's a feature request :)

[aristath]

Marked as a feature request.