add picture element data file
update spec url
update spec status. Looks like picture element is not an official spec by W3C. Somebody needs to review this commit
add demo link
add picture element support for IE. The spec url indicates that the implementation for IE is not there yet
The spec url indicates no information on implementation
update support for all the platforms. Almost all set to unknown
update keyword usage percentage
Merge pull request #487 from jaydeepw/picture

Picture element support data added