ENH: normalize by metadata
MAINT: remove unused import
DOC: fix typo
DOC: fix docstring (value is not a scalar)
ENH: Faster transform method (40x / 128x)

E.g., in a table of shape (1150, 108):
- axis = 'sample'
  new: 100 loops, best of 3: 3.35 ms per loop
  old: 10 loops, best of 3: 137 ms per loop
- axis = 'observation'
  new: 100 loops, best of 3: 7.51 ms per loop
  old: 1 loops, best of 3: 964 ms per loop
MAINT: remove leftovers from speed testing.
DOC: @wasade's suggestion
DOC: more docstrings, and a few improvements
ENH: Inplace transform, norm & norm_by_observation_by_metadata
TST: fix tests for in-place norm/transform/norm_by_...
Remove norm_by_metadata function and assoc tests
Merge pull request #337 from adamrp/norm_by_metadata

ENH: normalize by metadata
Merge branch 'master' into norm

Conflicts:
	biom/table.py
	tests/test_table.py
Merge pull request #338 from Jorge-C/norm

Excellent, thank you @Jorge-C
fix merge conflicts