:( gets converted to frowning, not disappointed
:D gets converted to grinning, not smiley

Plus, it's different now to :) becoming smile
Added .gitattributes
Allow img as emojify_tag_type

Allow img to be set as emojify_tag_type, this will also allow user to
retain emojify_tag_type in their config object by setting it to 'img'.
Previously user have to either unset the key, or set it to null, which
might be unintuitive.
Add tests for img as tag type
Update emojify.min.js
Merge commit 'e6bd9e4c8f459186d862130ee1afd238a88be4a0' into develop

Conflicts:
	emojify.min.js
Merge commit '1fc1e1bea076869663f39323af4343492b7658e3' into develop
Merge commit 'a664d908cd8aa5f6a3b593d0e65f2dca1d40422a' into develop
Merge commit '0f8d0abb03802578207f35fcd6245619d0b65a75' into develop