Add support for travis ci and tox

[aragilar]

This adds support for two testing utilities, tox and travis ci.

[bmcage]

Ok, I'm looking into moving to sundials 2.7.0 in light of the release. But it seems the code here does not redownload sundials?

export SUNDIALS_DIR=$HOME/sundials
SUNDIALS_LIBDIR=$SUNDIALS_DIR/lib
SUNDIALS_INCLUDEDIR=$SUNDIALS_DIR/include

if [ ! -d "$SUNDIALS_LIBDIR" ]; then
    mkdir -p $SUNDIALS_DIR
    echo "Installing sundials"
    ./ci_support/install_sundials.sh
else
    echo "Using cached sundials"
fi

Not sure how Travis works. It seems with a cached version, so how to remove that on new sundials version?

[bmcage]

I see only version in include/sundials_config.h.
Perhaps we should set here

export SUNDIALS_DIR=$HOME/sundials

to

export SUNDIALS_DIR=$HOME/sundials_2.7.0

then when 2.7.1 is released change this again. Good approach?

[aragilar]

Yeah, I wasn't expecting the 2.7 release (as I'd hardcoded many things), I've now added proper support for choosing the sundials version on travis (see #34). You may need to clear the cache before merging, but it should now be possible to choose which version to use just by modifying the .travis.yml file.

Also, Debian may soon have sundials 2.7, see https://lists.debian.org/debian-science/2016/10/msg00023.html and the rest of the thread (updating without dropping octave-sundials was one of the main reasons that I haven't finished updating sundials).