Experimental aura cache and accessors.

This should avoid "seq-scanning" the auras several times to find specific player auras.
UnitAura is not accessible in rules but there are specific accessors, e.g. GetPlayerBuff(unit, id), IterateDebuffs(unit), ...
Fixed aura iterators.
Update RulesRef.md
Update Rules.textile
Merge branch 'master' of github.com:Adirelle/AdiButtonAuras
Merge branch 'master' of https://github.com/Adirelle/AdiButtonAuras