doc + pep8
adapt pep8 test to changes in matplotlib pull request
Changed PEP8 test to flake8 test.

Also no longer depends on matplotlib.
Adapted setup.py
Refactoring
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
Removing duplicate test.
Many small changes so that the codebase adheres to flake8.

Mainly removing duplicate imports or unused imports.
Travis now uses flake8
Merging with master
Merge pull request #644 from krischer/flake8_tests

Flake8 tests
Merge pull request #559 from megies/resource_id_prefix

check ResourceIdentifier/public_id handling in event/QuakeML output
Added flake8 test to the changelog
minor adjustments for new flake8 testing
use 2*wlen+1 instead of 2*wlen for creation of taper_sides
refactoring