Added links to capabilities docs
Merge pull request #20 from anton-rudeshko/patch-1

Added links to capabilities docs
Change format of browsers config option from array to object

This change is needed to gain an ability to specify all the needed list
of capabilites to the every single browser.

Object structure:
- keys are browser identifiers
- values are browser capabilities (`browserName`, `version`, etc)
Use capabilities format object for skip()
Rename Browser.prototype.name to id
Allow setting of browserName and version shared capabilities
Update readme
Merge pull request #23 from bem/feature/browser-caps

Change format of browsers config option from array to object.

This allows to specify all required capabilities for browsers, not just name and version.
fixed grammar error
Merge pull request #24 from lapinlapin/master

doc: Fixed grammar error
Calculate capture rect in browser

This allows to save some network overhead (1 request vs 4 request per
element). Plus, it allows to do some preparations to screenshot capture
in future commits (i.e. scroll screenshot rect to be fully visible).
WIP: Works for out of viewport elements

Many browsers are unable to capture screenshot of whole page and
capturing only viewport. In this case, we are scrolling test rect into
view before taking screenshot and comparing image size with body size
performing appropriate crop.