* doc/bison.texinfo (Push Decl): Document the push parser.

(Table of Symbols): Ditto.
(Pure Decl): Ditto.
(Decl Summary): Ditto.
(Multiple Parsers, Push Parser Function, Pull Parser Function,
Parser Create Function, Parser Delete Function):
Add new push parser symbols.
(Table of Symbols): Document push-parser, push-pull-parser,
yypush_parse, yypull_parse, yypstate_new and yypstate_delete.