muscle: check the kind of api.prefix, api.location.type

* data/bison.m4: Check api.prefix.
* data/c++.m4: Check api.location.type.
* doc/bison.texi: Fix uses of api.value.type, api.prefix, api.location.type.
Document {...} values for %define.
* src/parse-gram.y: Fix use of api.prefix.
* tests/calc.at: Fix uses of api.location.type.
* tests/input.at: Check api.prefix, and api.location.type.

src/parse-gram.y

@@ -82,7 +82,7 @@ static char const *char_name (char);
   #define YYTYPE_UINT8 uint_fast8_t
 }
 
-%define api.prefix "gram_"
+%define api.prefix {gram_}
 %define api.pure full
 %define locations
 %define parse.error verbose