Lemon updates: (1) include the #defines for all tokens in the generated C

Lemon updates:  (1) include the #defines for all tokens in the generated C
file, so that the C-file can be stand-alone.  (2) If the grammar begins with
a %include {...} directive on line one, make that directive the header for
the generated C file.  (3) Enhance the lemon.html documentation.

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