Added ignoreFiles option, corrected camelcases

Added ignoreFiles option which allows you to ignore certain files containing a string.
Renamded starttag and endtag to startTag and endTag.

Merged Pullrequests #3, #4, #5
Fixes #3
Fixes #4
Fixed #5

If you want to use this build, use `"grunt-injector": "git://github.com/leipert/grunt-injector.git"` in your `package.json`