Move library files in src/ to new directory qsopt_ex/

This means that header files can be referenced in the same way as
when in installed, using `<qsopt_ex/XX.h>`. This means that programs
and the Python module can more easily be built separately.

The esolver program file is split off into esolver/ and the test
programs eg_sloan and demo_qs are split off into tests/.
Add setup.py script to build Python module independently

The setup.py script is based on distutils. When building the module
using the autotools build system, the module will depend on the
simultaneously built libqsopt_ex. This build script can be used
to build and install the Python module based on the libqsopt_ex
that is already installed on the system. This makes building and
packaging easier in some cases, particularly when packaging for
various distributions.