Add changes for chrome support

[daviirodrig]

I made two change for this to work on chrome, following the MDN guide building a cross-browser extension

• Change API namespace to chrome.*
• Change the asynchronous event handling to callbacks instead of promises

Resolves #9

[54ac]

Have you tested whether it works at all?

[daviirodrig]

Oh yes, sorry for not mentioning this in the PR. I tested on chrome and firefox and surprisingly both works well in my tests

I first started doing the porting just for my use but it turned to work so well with not so much changes that I made this pull request.

[54ac]

Cool, that's quite surprising. If I ever decide to pay the registration fee, at least there won't be much work additional work to be done. Thanks.

[smaragdus]

@rowrawer

Any chance to publish a CRX file in the Releases page?

[54ac]

I'll look into it.

[smaragdus]

@rowrawer

Thanks.