BUG: Fixed _format_labels in tile.py for np.inf.
Fixes issue https://github.com/pydata/pandas/issues/3415.

can you squash to 1 commit? looks good 
 if you want to put you test example in v0.13.0 you can (to sort of 'announce' this fix)..up2u
 I did that, I hope adding the example to the documentation is okay.

One question: It's rather unmathematical to write `(0, inf]` (i.e. closed at infinity). Should we be correct about this and make the label `(0, inf)`, resp. `(-inf, 0)`, or do we prefer the uniformity?
 @jtratner @cpcloud ?
 @filmor Can u rebase?
 Done. The question still stands though, but it can be handled in a different PR.
 I think it's more consistent to use the existing labeling scheme (even if technically mathematically incorrect)
 That's fine with me :)
 @filmor thanks!
