Mathics-pygments

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Reorder list of REs tried so that Symbols re comes before Identifier
regular expression.

This corrects symbol detection and "<<" or ``Get[]`` detection.

(There are still two classes lexer tests that need to be addressed to
be on par with pygments-mathematica).

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* Fix RE's that I had messed up in initial port for Slots, Patterns and Named Characters
* Make ujson optional. This makes this runnable from pyston 2.2

Note: There are still a few tests from pygments-mathematica that fail.

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First public release. Is largely the same thing as
pygments-mathematica, but we are geared for CLI use in mathicsscript and
we get operator information from Mathics Scanner.

For uses outside of terminal use, pygments-mathematica is probably better.
But over time I expect this will change since we will draw more power from
Mathics Scanner.