Replace HTMLEntities gem

[skalee]

We use https://github.com/threedaymonk/htmlentities gem in some places. Let's replace it.

• This gem is slow as hell when used improperly (instantiates the same regexp over and over again, and that involves parsing its source)
• This gem isn't thread-safe
• This gem is no longer maintained (last release in 2015)
• This gem fails to recognize entities in some edge cases (bug reported 3ys ago)

Ridiculously, this gem has 80 millions downloads…

[ronaldtse]

Agree. @skalee what's the alternative (gem)?

[skalee]

I don't know any alternative, but official list of entities is available as JSON, so writing a new one should be easy. I'm not yet sure if we really need that though.