This is something that a lot of applications will probably have to
implement anyway, so we might as well provide it and do it within Rusts
standard traits.

This does not provide localization, but it uses the English names, which
should be good enough for most cases.

Since we provide FromStr for those classes as well, it makes
double-sense to add Display. However, not all cases are currently
reversible ("Cairn the Indomitable" vs "Cairn"), although the status quo
seems fine for now (most people type Cairn, but when outputting we can
use the full name).

The given buff is the Countdown effect that each player has:
https://wiki.guildwars2.com/index.php?title=Countdown

The logic is from GW2-Elite-Insights-Parser (Cairn.cs, IsCM), but we
count this as a buff instead of a skill.

This is the start of an effort to clean up lib.rs a bit by moving out
functions into their own module and re-exporting them.

This still needs a bit of work, as some of them are untested (Conjured
Amalgamate, Fractal CMs).