Cpymad

- suppress internal stack traces
- raise exception for failed twiss instead of returning invalid table that
will crash later on
- fix incorrect ``Element.position`` attribute for sequences with
``refer=entry`` or ``refer=exit``
- allow passing parameters with underscore suffix to commands, this allows
passing parameters as bare words that conflict with python keywords (e.g.
``madx.command.select(class_='quadrupole')``
- improve ``repr()`` for ``Table``: show column names

- allow redirection of MAD-X standard I/O via Madx constructor

- ignore comment markers within string literals (121)

- migrate to setuptools from distutils
- python3 support
- add continuous integration with Travis
- proper setup.py and MANIFEST.in to be used with PyPI
- rename package to 'cern-pymad'
- allow to build from PyPI without having cython

- fix error in ``get_copyright_notice`` due to backward incompatible API
changes of ``importlib_resources``. This function now requires py>=3.7,
as supporting it for lower python versions would be unwarranted effort.

- change ``Madx.beam`` to provide access to the current default beam instead
of simply deferring to the ``BEAM`` base command. You can still use it as
command though.
- add mapping ``Madx.beams`` to provide access to all defined beams by name,
similar to how ``Madx.table`` and ``Madx.sequence`` currently work.