add support for optional catch binding

[cixel]

Fixes #382.

Tests rely on esprima 1953 or they will throw early:

  1) general test try statement:
     AssertionError: expected [Function] to not throw an error but 'Error: Line 1: Unexpected token {' was thrown
      at testIdentity (test/test.js:14946:23)
      at runTest (test/test.js:14974:9)
      at test/test.js:14983:17
      at Array.forEach (<anonymous>)
      at Context.<anonymous> (test/test.js:14981:41)

This PR can hibernate until there's progress on esprima's end, and until esprima dependency version bumps to 4.x+.

[sanex3339]

Any update on this?

[sanex3339]

@cixel

[sanex3339]

#398 is merged
Can you update this PR?

[sanex3339]

If here will be no actions in the next few hours, i'll recreate this PR with updated esprima dependency.

[cixel]

Sorry, I've been away. It may be simplest for you to recreate the PR, I haven't touched this stuff in a while.

[sanex3339]

Yep. I already did
#403

[cixel]

Good stuff. Thanks!