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
Tags cannot start with a digit.
Merge pull request #8 from dchest/letter

Tags cannot start with a digit
Look for @jsx pragma natively, rather than with grep

Fixes #13.
Add option to disable requiring @jsx pragma matching

Also fix use of silent!
Use the *search* function to detect the pragma
Merge pull request #14 from baskerville/master

Use the *search* function to detect the pragma
Cleanup
Call the search function with the wrapping flag on

There's a (very improbable) user configuration that could make the
detection fail without this flag:
    autocmd BufReadPost * exe "normal! '\""
    set nowrapscan
Merge pull request #15 from baskerville/master

Call the search function with the wrapping flag on
Add support for namespaced JSX Tags (available since React 0.11)