Make Madx.command a MadxCommands instance.

This is a fully backward compatible change.

The advantage is, that Madx.command now gives access to raw variants of
MAD-X commands, e.g.:

>>> madx.command('twiss', ...)
>>> madx.command.twiss(...)

Will just take all parameters, generically create a MAD-X command string
from them and issue them in the interpretor, without any special
treatment whatsoever.
Add more generic function mad_command

The new function should be used in favor of the now deprecated
_mad_command function.
Use the new simplified .command internally

This should be mostly backward compatible. One excepton is .match which
used _mad_command before.
Remove obsolete functions in _madx_tools
Remove tmpfile treatments

Madx.match does not return the results anymore.