DOC: add note about efficiency
ENH: add warning module

I was going for an ad hoc warning, but @gregcaporaso mentioned it could
be useful for other stuff.
ENH: Raise EfficiencyWarning
MAINT: reorder imports
MAINT: Don't bother assigning to `_`
MAINT: filter warnings (needs nose runner)
ENH: skip whole class if import didn't work
STY
BUG: There was a implicit relative import waiting to bite
DOC: document that absolute imports are a *very* good idea
Merge pull request #350 from Jorge-C/so

.so