Refactored stdev transform to be applied to multiple fields, not just price
UnitTest for transforms refactored to account for changed stdev transform, introduced AssertAlmostEqual

Signed-off-by: Elektra58 <fpsteiner@gmail.com>

Here with flake8 compliance
Again, pep8 compliant, unittest imports rolled back

Signed-off-by: Elektra58 <fpsteiner@gmail.com>
Merge branch 'master' of https://github.com/Elektra58/zipline

Conflicts:
	tests/test_transforms.py
	zipline/transforms/stddev.py