changelog
add keywords max_percentage=0.05, max_length=None for taper method of Trace
adjust taper tests
add test for teper length
doc + pep8
extent taper length test
adjust doc
correct test, it fails actually, taper is one sample too long on left
side
refactoring
overlong tapers were not corrected actually (only the warning shown ;))

 - also add basic test for overlong taper
minor adjustments for new flake8 testing
use 2*wlen+1 instead of 2*wlen for creation of taper_sides
refactoring
Attempting to fix travis
adjust test and remove one superfluous int()
PEP8
Merge pull request #642 from obspy/taper_length

using tapers function with "percentage" option