Python-only version of bob.measure

This MR implements the following changes to this library, in an API backward-compatible way:

1. Minimize the number of Bob dependencies to a bare minimum. Use h5py to read data, RNGs and linear algebra from numpy. Remove requirements for bob.core, bob.io.base, bob.blitz, and most of bob.math (except for the PAVX algorithm)
2. Remove deprecated dependencies (docopt)
3. Use pytest for tests instead of nose
4. Re-implement the old C++ as a Python-only library (remove all C++ dependencies such as Boost)