Treat arguments specially.

Summary: They are now matched as a block instead of one at a time. This saves a huge number of guesses when there are wildcards in an argument list.

Test Plan:
Run test suite
Test simple Snowman in structuredJS demo page

Reviewers: john, pamela

Subscribers: #cs

Differential Revision: https://phabricator.khanacademy.org/D14981