issue with parsing negative numbers with no digit before the decimal point

[pjfanning]

An example is '-.125'. This is not valid in standard JSON but jackson has JsonReadFeature.ALLOW_LEADING_DECIMAL_POINT_FOR_NUMBERS to allow it. The feature works for positive numbers but not for negative numbers.

See #777 and #781 for failing tests

[cowtowncoder]

Was able to solve the case for UTF8StreamJsonParser, code differs a bit with others but hope to do the same.
This will also include + in getText() (at least for the case I fixed).

[cowtowncoder]

UTF8DataInputJsonParser similar to UTF8StreamJsonParser so fixing that easy too.
Tricky case is ReaderBasedJsonParser since it tries to optimize things, trying to reuse input buffer (that is, avoid use of TextBuffer) and then has to worry about buffer boundary conditions.

[cowtowncoder]

Was able to fix reader case easily as well.

But looking at code I am fairly certain that it won't work for all cases, especially with buffer boundary conditions.
I think I'll try to extend tests to try to catch such cases, although I guess Fuzz-testing would work best for stuff like this.