Add a url option when executing image action

[minhnhatspk]

Q	A
Bug fix?	no
New feature?	yes
BC breaks?	no
Deprecations?	no
New tests added?	not needed
Fixed tickets	no
License	MIT

Description

[Description of the bug or feature]
when i use execAction('image'), i don't see any options in your guide to put an url to this method.
so i decided to create my own one.
my use case: I handled image from clipboard, upload it to server and response an url, then i show it on medium editor by execAction('image',{url: 'https://mywebsite.com/example.jpg'}).
if you see it useful, you can merge this request.
and if my changed is bad, please improve it and update your readme.md.
Thank.

--

[coveralls]

Coverage remained the same at 94.469% when pulling b10b7a3 on minhnhatspk:master into 3fcd1b2 on yabwe:master.

[j0k3r]

Could you revert the dist/* changes?
Could you also add a test to cover the options url attributes?
Thanks