Single ~ is not accepted for strikethrough

[cometeer]

Despite being reasonably common in multiple markdown specs, using a single ~ does not render strikethrough text.

[amit-chaudhari1]

Thanks for bringing this up, I'll implement the ~ strikethrough for sure...

@RobertDober Do we aim for following a specific spec ?
Remember reading somewhere in our issues about John Gruber's spec?

#390 (comment)

I could write some tests that make sure we comply with the whole spec. Please let me know which spec

[RobertDober]

@RobertDober Do we aim for following a specific spec ?
I did not, but tried to follow trends from issues, so we got quite GFMish but honestly there are some rough edges concerning specific uncommon issues.

Concerning the single ~ I'd probably put it high prio if someone asked in the EarmarkParser for it