Add initial attempt at travis.yml

We'd like to take advantage of travis.
Specify value of DOXYGEN variable
Install doxygen from apt-get before testing
Remove python 3.2 from travis builds

As it doesn't support u'' prefix I think most projects have stopped
bothering to be compatible with it.
Remove pdb (-P) flag from travis builds

We make it overridable and override it for the travis builds to an
empty string.
Switch to subprocess.Popen

For python-2.6 compatibility.
Use 'as' syntax for Py3 compatibility
Use relative import for Py3 compatibility
Switch string to unicode for Py3 compatibility
Configure travis to install breathe and use that

Rather than changing the system path to look at the local code, we
install that and rely on it being picked up from the virtualenv.

This is because the install process should use 2to3 to convert the code
for the python 3 environments which is required. Simply pointing the
python3 sphinx at the local breathe results in errors from the Python2
syntax and imports.
Add travis badge to README
Merge branch 'travis'