Added regex sub rule for String.format - #18

I'm fine with this, but it's going to have to get rewritten as an AST transformation. We just got bit by a bug where the regex didn't replace .length() properly when used inside an expression, and this might have similar problems.

Also, Format.java should be Format0.java, but I'll fix that.

Does not handle the whole Java specs about Formatter, like %1$d

"{1:d}".format() does though

Great. I'm investigating this correspondence. Pretty hairy it seems.

Would be great if you guys could find some time to review commit 6a8ded2
It's intended to be a first iteration for this feature. It satisfies the Format0 test case (updated).
(Are implemented argument index and conversion id.)

(And please suggest a better place for the helper func. formatSyntaxTransf(match))