Concurrent formatters

[Diego Belfer]

Hello,

I was thinking of working on trying to convert the code of some of the
formatters DecimalFormatter, SimpleDateFormatter, etc to allow concurrent
calls to the format and parse methods.
I know it has been discussed many times in the forums and I understand they
were not initially designed for that, but it does not seem very difficult
at first glance to attempt to make this enhancement.

What do you think? Have you already tried to accomplish this and found some
blocking issues?
Do you think this change would make the API documentation confusing ?

Best,
Diego Belfer [muralx]