browserify as peer dependency
Fix crash on karma config without browserify property

Fixes this error:

    node_modules/karma-browserify/lib/index.js:148
        extensions: config.extension,
                      ^
    TypeError: Cannot read property 'extension' of undefined
        at configuredBrowserify

If your karma config module doesn't have a "browserify" property at all.

Uses mostly coffeescript function argument default value syntax
Adds badges and license to README.md
Relaxes dependencies.
Merge commit 'd4fd73613a511d8a0b8272f9f798bc764381929b'
Merge commit 'b1b33a5bbd11b38e03ffd7c6ffdbdd7bba86840d'
Adds contributors.