Filterbank
Numpy installation less verbose
Skip build and .tox directories in tests
Octave: Have certain methods available as seperate functions

* New functions
* Reference value is now module constant (soon we should merge these
module constants that are spread across the different modules)
* Rewrote properties using decorator syntax
Merge branch 'master' of github.com:python-acoustics/python-acoustics into octave
Merge pull request #34 from FRidh/octave

Octave
Travis: Remove testing of 1.6

* Don't support 1.6 anymore. This version is nearly 3 years old by now.
* Remove minor version numbers. This might make it harder to track
whether the error is on our side or due to a changed api of our
dependencies.
Merge pull request #36 from FRidh/travis

Travis: Remove testing of 1.6
Setup: Update dependencies
Merge pull request #35 from FRidh/setup

Setup: Update dependencies
Merge branch 'master' of github.com:python-acoustics/python-acoustics into filterbank
Filterbank: Frequencies classes and further implementation of the filterbank

Not validated yet!