* lily/my-lily-parser.cc (parse_string): init parser variable when

* lily/my-lily-parser.cc (parse_string): init parser variable when
lexer_ is set, ie. in parse_string and parse_file.

* scm/lily.scm (collect-scores-for-book): new function.

* lily/my-lily-parser.cc (LY_DEFINE): define parser in parser
scope, not in lily module.