Use `HexIntegerLiteral`s for Unicode code points

When referring to Unicode code point values, it’s easier to stick to
hexadecimal notation. This patch makes sure we do it consistently.

https://code.google.com/p/esprima/issues/detail?id=477
Present diffs for mismatched actual and expected JSON.

https://code.google.com/p/esprima/issues/detail?id=478
Update some files in the benchmark corpus.

Updated libraries:
  - AngularJS 1.2.5
  - Backbone 1.1.0

https://code.google.com/p/esprima/issues/detail?id=354
Add "--strict-json" flag to tools/generate-test-fixture.js

Currently tools/generate-test-fixture.js outputs JSON objects whose keys are not
double-quoted. This changes the tool to accept a `--strict-json` argument which
indicates that it should always double-quote object keys.

This is useful for piping the output of generate-test-fixture.js to other
tools that expect valid JSON.

https://code.google.com/p/esprima/issues/detail?id=461
Travis CI: Skip building on Node.js 0.6.

The new library optimist for tools/generate-test-fixture.js causes a
module install error.

https://code.google.com/p/esprima/issues/detail?id=461
Add "node_modules" folder to .gitignore

https://code.google.com/p/esprima/issues/detail?id=482
Make npm test work on Windows and ignore node_modules directory

https://code.google.com/p/esprima/issues/detail?id=490
Update ESLint to 0.3.0.

https://code.google.com/p/esprima/issues/detail?id=473
Link to the issue tracker from the package manifest

https://code.google.com/p/esprima/issues/detail?id=491
Use JSCS to check the coding style.

https://code.google.com/p/esprima/issues/detail?id=492
Fix running Backbone in the quick benchmark.

https://code.google.com/p/esprima/issues/detail?id=354
Update ESLint to 0.4.2.

https://code.google.com/p/esprima/issues/detail?id=473
Fix the issue when the loc/range would sometimes include a leading whitespace.

Summary:https://code.google.com/p/esprima/issues/detail?id=501
markStart() was not always preceded by skipComment(). Moving the
skipComment() inside instead.

Test Plan: npm test
Update jQuery Mobile in the benchmark corpus to version 1.4.2.

https://code.google.com/p/esprima/issues/detail?id=354
Merge branch 'master' into gh-pages