HTML tag highlight added.

Tag highlight functionality added.

![Image](https://lh6.googleusercontent.com/-3nfFux6Tzqc/UeeF9Tw5bhI/AAAAAAAAAfg/BHwiUV271ac/s335/HTML%2520Tag%2520Highlight%2520pull%2520request.png)

***some tracks***
[Google Group Discussion](https://groups.google.com/forum/#!topic/brackets-dev/Dl9mOPBNQUA)
[Trello Card](https://trello.com/c/rhKIGceF)
https://github.com/adobe/brackets/issues/3069

Code mirror's [matchTags extension](https://github.com/marijnh/CodeMirror/blob/master/addon/edit/matchtags.js) only highlight the other tag. In the above screenshot, i put cursor on start tag &lt;form, but it only highlights the other tag &lt;/form&gt;. If you want to to highlight both tags, i can rewrite this extension for brackets.