Added picture width and height attributes copying

Both picture and image elements allows to specify dimensions.
http://www.w3.org/TR/html-picture-element/#the-picture-element
Fixed width/height/alt nulls
Merge pull request #8 from kolesnikovde/image_dimensions

Added picture width and height attributes copying
Added new performance comparison test, deleted old
Deleted old performance comparison files
Revert "Merge pull request #8 from kolesnikovde/image_dimensions"

This reverts commit 61b6ccad213f05c4c76c66471bf715cfac834e72, reversing
changes made to 23782ce0fabf8c995db9191ffbd88f3c2d2aacd0.
Releasing 3.3.0, picture width and height to img

Releasing 3.3.0, which copies picture's width and height attributes to
the resulting image
Fixed image reloading
Merge branch 'pr/9'
Version bump to 3.3.1
Releasing 3.3.2, fixes #7
Updated version in readme title
Version bump to 3.3.3
Removed obvious statement
Releasing version 3.3.3: fixed a bug when using picturePolyfill together with the matchMedia polyfill
Releasing v3.4.0

v3.4.0 gives the user the ability to parse() the DOM without reading
from picturePolyfill’s internal cache
Merge branch 'master' into gh-pages