Update package.json.

* Use tilde versions for dependencies
* Explicitly set the files to install
* Use the standard `license` property
* Remove unneeded main property
* Remove unneeded "grunt.js" keyword
Minor README.md tweaks.
README.md: switch to SVG badges.
Bump version to 0.4.2.
Merge pull request #56 from XhmikosR/master

Update package.json