Markdown autolinks <url>
Let the short version of links not have title

and create versions with title with "

Rationale: it is more common to have links without title in Markdown.
Fix markdown fenced code blocks.

Broken because backticks were interpreted as vim code execution.

Also simplified the trigger which was too long and unintuitive.
Merge pull request #483 from cirosantilli/markdown-autolink

Markdown autolinks <url>
Merge pull request #486 from cirosantilli/markdown-link-no-title

Let the short version of links not have title
Merge pull request #487 from cirosantilli/markdown-fix-fenced

Fix markdown fenced code blocks.
Make markdown links consistent on cursor exits

Make the versions of link with and without * behave alike:

-   don't set the 0 location so that the cursor exits.
    Having a 0 in the title is bad because titles are short.

-   either open a new line at end for both, or for neither

    The only case where the newline is certain is for link definitions.