* doc/bison.texinfo: Fix some typos.

* doc/bison.texinfo: Fix some typos.
(GLR Semantic Actions): New subsection discussing special
considerations because GLR semantic actions might be deferred.
(Actions): Mention look-ahead usage of yylval.
(Actions and Locations): Mention look-ahead usage of yylloc.
(Special Features for Use in Actions): Add YYEOF entry and mention it
in the yychar entry.
In the yychar entry, remove mention of the local yychar case (pure
parser) since this is irrelevant information when writing semantic
actions and since it's already discussed in `Bison Symbols' where
yychar is otherwise described as an external variable.
In the yychar entry, don't call it the `current' look-ahead since it
isn't when semantic actions are deferred.
In the yychar and yyclearin entries, add note about deferred semantic
actions.
Add yylloc and yylval entries discussing look-ahead usage.
(Look-Ahead Tokens): When discussing yychar, don't call it the
`current' look-ahead, and do mention yylval and yylloc.
(Error Recovery): Cross-reference `Action Features' when mentioning
yyclearin.
(Bison Symbols): In the yychar entry, don't call it the `current'
look-ahead.
In the yylloc and yylval entries, mention look-ahead usage.