parse: run parse.js through the linter.
parse: move parse.js under parse/.
parse: make r5js.Parser a @struct and clean up imports.
misc: rename r5js.Parser => r5js.ParserImpl.
parse: the file containing r5js.ParserImpl should be named parser_impl.js.
parse+misc: rename r5js.IParser interface to just r5js.Parser.
parse: the file containing r5js.Parser should be named parser.js.