Add overrides option to override handlebars public API functions.

This will let you override handlebars [public API functions](https://github.com/wycats/handlebars.js/blob/7f6ef1dd38794f12aee33c76c04f604a7651810b/lib/handlebars/compiler/javascript-compiler.js#L10) in your brunch-config file.
Update README to include the overrides plugin option.
Merge pull request #21 from elving/master

Add overrides option to override handlebars public API functions.
global namespace setting
add global namespace test
fix: combined assignment and conditional
Merge pull request #22 from f-kubotar/namespace

Global template object support
Drop coffeescript, update handlebars.
Release 1.7.3.
Release 1.7.4.
Release 1.7.4.
Make path replace configurable
Fix indentation
Merge pull request #24 from urosgruber/config-replace

Make path replace configurable
Upgrade handlebars to 1.2.1. Resolves #25
Release 1.7.5.
Include runtime directly from npm module files
Configurable include file. Resolves #19
Fix includeFile references
Document include options