add some installation instructions

Add a rzSliderShowTicks and rzSliderShowTicksValue

package.json main field corrected

minor improvement

reason:
when the *ceil value* is `0` and the *model value* is `0`, the `valueToOffset` function returns `NaN`.
And the *low handle* label has a litter poor display.
the `single.html` shows the problem

* add `'use strict'` declaration
* update some docs
* optimize line#L423
* update line#L243-L251's format
* add .editorConfig file whose config is based on current sourcefile

Remove unnecessary dependency

Add umd support. Extract template in its own file.

take the *html fragment* out of the js file, and use *grunt-angular-templates* and *grunt-replace* plugin to generate the templateCache and insert it into the js file

On click, move the handle closest to the event

Fixes issue #101.

Draggable range

Add a rzSliderOnChange attribute.