Relax base dependency to <4.8

New GHC is stabilised in Gentoo, and it works well.

The change in Units.hs is necessary due to a regression in GHC (so maybe
it doesn't work *that* well, LOL). The type constraint was unnecessary
anyway -- the TimeUnit constraint may be inferred by the "class Timeunit
t".

Signed-off-by: Alexander Berntsen <alexander@plaimi.net>
Signed-off-by: Stian Ellingsen <stian@plaimi.net>
Reviewed-by: Stian Ellingsen <stian@plaimi.net>
Bump to 0.2.2

Signed-off-by: Alexander Berntsen <alexander@plaimi.net>
Signed-off-by: Stian Ellingsen <stian@plaimi.net>
Reviewed-by: Stian Ellingsen <stian@plaimi.net>