replace "is" with pair of brackets (imgur)

What imgur calls "title" is possibly better described as a caption. Most titles in imgur's gallery are full sentences, making the current behaviour of "xxx is yyy" fall flat, as the resulting string does not have satisfactory grammar.

This commit changes the functionality from "[foo is bar]" to "[foo][bar]".

Untested.
Merge pull request #365 from zuzak/patch-4

replace "is" with pair of brackets (imgur)