Do not consider << as a start tag.

This is, of course, not ideal, as mentioned in #5, but having a right
shift operator followed by a number or identifier is more common than a
less than operator followed by JSX tag.
Enable JSX syntax/indent only when @jsx pragma is found

Fixes #7; fixes #9.
Merge pull request #6 from dchest/patch-1

Do not consider << to be a tag start