add basic population spike analysis module
pep8 check on gridcells.analysis.spikes (+tests)
add bump analysis module: analysis.bumps
pep8 on analysis.bumps and analysis.spikes
add tests for sliding firing rate computation

This also fixes a bug in which returned times array could be one longer than
the firing rate array.
clean up spike analysis tests
clean up bump fitting tests
pylint on analysis.{bumps|spikes} + improved docs
update tox.ini to work on local machines from scratch
add tests for analysis.bumps.SingleBumpPopulation
Merge branch 'new-spike-analysis'

Conflicts:
	doc/src/modules/index.rst