add switch for HDF5 dependency

in principle, we could create different versions for pypi, with or
without the dependency on HDF5.
I'm not sure how to do that though...
apply 2to3 to all files

i.e. make the package compatibile with python3.
bugfix --- check python major version in cutout.py
bugfix --- fix python3 incompatibilities
move license text a bit
make license text the same for all files
remove redundant descriptions
add sympy dependency to setup.py
move installation instructions in readme

I figured we can always separate them in the future if that's to be
desired.
fix README markup thing
bugfix --- spline test works now
add tests to call through setup.py
import generic_splines test

well, it's a really basic test, but it's the best I could come up with.
add call to generic_splines test

just to make sure that sympy is installed properly
add call to test_cutout
add tox configuration

apparently, you don't need virtualbox to test python packages.
add .tox to .gitignore
add call to tests for tox

so basically now I should only need to execute one command to test the
entire thing on different distributions...
use bools for package checks

also, make generic spline test print out weight functions if matplotlib
is not present on the system.
Merge branch 'develop'