Many improvements

[igoradamenko]

Hi!

This PR is about #2 & #9.

• Test was rewritten to mocha & expect.js;
• .gitignore & .npmignore were added;
• Parsing of centre & grey are rewritten, 'cause for instance background can be set to grey url(..) centre and previous parsing missed this;
• Added storey support;
• Some improvements in README.

Also I'm not sure that media == medium, but I'm not guru in English :)

P. S.: If it's alright, don't forget about a version bumping!

[hashanp]

Merged :smiley:. The lastest version is available on NPM at 0.1.0. Thank you very much.