Don't add pairs if the next char is alphanumeric

[Balrrach]

I'd would be great to have ana option to not add a pair if the next character is alphanumeric like windwp/nvim-autopairs implements.
Great job with thw plug-in, congrats!

[LunarWatcher]

#177, #194, and I remember there being more.

My fork supports this (see |migrating|), with the implementation merged in from this (now dead) fork. See also #309

[Balrrach]

Ok, thanks!