Teach the lexer/parser to recognize and decode them in JSON5 mode.
Teach the encoder to use them in JSON5 mode.
Add another error message for bad hex digits.
Test cases to show they work, and that the bad-digit check fires.
Any character other than the digits 1-9 may be preceded by a
reverse solidus '\', and unless the combination has an explicitly
defined expansion the character is included without the solidus.
JSON5 adds \', \0 and \v to the set of defined escapes, and an
escaped newline is omitted from a string.
In the test case Perl uses \13 instead of \v in the output
but it is the correct character (13 octal = 11 decimal = '\v').
Adds another lexer entry point for lexing map keys only,
adjust parser to use this instead of the general lexer.
Also defines another lexer token for internal use only.
NaN and both Infinities, with tests.
Special handling was added to yajl_test since different OSs don't
always generate the same output for special numbers (nan/NaN/...).
If configured for JSON5 the lexer now allows a leading or trailing
decimal point on doubles, and an explicit leading + sign on integers
or double numbers.
Includes test cases.
