A minor release, mainly aimed at releasing a version with go.mod.

• Added go.mod
• Enhanced support for info strings in fenced code blocks (issue #410)
• README updates
• Added a reference to confluence wiki renderer
• Fixed HTML entity regex
• Fixed HTML5 by removing rel="footnote" which is invalid
• Added NoopenerLinks option that adds rel="noopener" attribute
• Added heading offset option to HTML renderer
• Fixed consecutive lists of different kinds
• Fixed block parsing for fenced code blocks in lists (issue #239)

Huge thanks to the contributors!
Bjørn Erik Pedersen (@bep)
Cameron Moore (@moorereason)
Dmitri Shuralyov (@dmitshur)
Emil Melnikov (@emilmelnikov)
Iain Haslam (@understated)
Kentaro Matsushita (@kentaro-m)
Liming Jin (@jinliming2)
Michael (@michael-k)
Mitchell Cohen (@mitchchn)
Nathan Glenn (@garfieldnate)
Nick Galbreath (@client9)
Rebecca Turner (@9999years)
Vas Sudanagunta (@vassudanagunta)