More flexible column detection in complex format strings

[staticglobal]

python printf-style format strings, such as those used by the logging
formatter, have provisions for many advanced field conversions such as
field widths, padding characters, etc. For example, you can force the
"msecs" to always be a zero-padded 3-digit field by specifying
"%(msecs)03d". However, modifiers such as these breaks
rainbow_logging_handler which is looking for a strict string match for
"%(msecs)d".

This change enhances rainbow_logging_handler to detect and cope with
(almost) any field conversion modifiers and still apply the appropriate
colors.

[staticglobal]

Also adds a new dependency on the "re" standard library

[miohtama]

Hi!

I am taking over the library maintenance. Can you please add an automated test case to stress out this functonality and it's good to merge.

[jclosure]

+1 - for this feature. The current date stamp format doesn't support the ms precision we need.