fix: autolink option should not apply on markdown syntax

[curbengh]

link renderer method couldn't discern whether a link is inside [](), <>, http://example.com or www.example.com.

Meanwhile, url tokenizer is the method responsible for detecting http://example.com or www.example.com, so autolink option is more suitable there. (marked doesn't detect example.com, if a link doesn't starts with protocol (e.g. http://), a link must starts with www to be detected).

Fixes #139

[coveralls]

Coverage decreased (-2.2%) to 97.849% when pulling 40d8204 on curbengh:fix-autolink into 29b49aa on hexojs:master.