Improved syntax, and added new instructions to the JTL interpreter.

Added 5 new commands to the JTL interpreter. Also fixed a few nits, typos, tests, and clarified some comments in existing code, as well as changed the syntax so JTL programs became a lot more readable.

BUG=298036

Review URL: https://codereview.chromium.org/35353002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@231019 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 231019