Parse role mentions appropriately, as with channel and user mentions

[Throne3d]

Description

As requested in #186, translate role mentions appropriately between IRC and Discord. This works both ways, so the numbers will be translated into proper text when outputted in IRC, and the plain-text mentions will be made into proper role mentions when outputted in Discord, if (and only if) the role is mentionable.

Present behavior

As in #186, using e.g. @sysadmin in Discord will end up outputting a long string into IRC, e.g. <@&233558485999…>. In addition, using @sysadmin in IRC will not produce a mention in Discord, even if the sysadmin role is mentionable.

Modified behavior

If newrole is not mentionable and otherrole is mentionable, the following output is produced in Discord:

Throne3d wrote:
@newrole

IrcBridge wrote:
<Throne> @newrole
<Throne> @otherrole # actually works

Throne3d wrote:
@otherrole # actually works

and in IRC:

<test2> <Throne3d> @newrole
<Throne> @newrole
<Throne> @otherrole
<test2> <Throne3d> @otherrole

I wasn't sure how exactly to set up the tests (you may note the first commit, a1dfdf6, sets up a const getRole in bot.test.js, which is later removed in favor of a this.findRoleStub, behaving somewhat like this.findUserStub), but they seem to pass where appropriate and match the style of the other tests at least reasonably well.

This should solve #186.

[coveralls]

Coverage increased (+0.1%) to 97.452% when pulling b30c4c3 on Throne3d:add/role-mentions into 26626e5 on reactiflux:master.

[ekmartin]

Beautiful pull request - thank you!

[ekmartin]

Released in 2.3.0!