update udev rules

With usbtmc driver being classified under usbmisc in newer kernels the udev rules
need an update.
probe_groups: API changes required to implement probe groups.
Use priv for consistency
probe_groups: Update Python bindings for API change.
probe_groups: initialise sdi->probe_groups to NULL.
probe_groups: Add a name field to sr_probe_group.
rigol-ds1xx2: create probe groups.
rigol-ds1xx2: implement probe group specific options.
python: Add classes for probes and probe groups.
python: Map probe group configuration to ProbeGroup attributes.
rigol-ds1xx2: Skip obsolete fields
Update API documentation
rigol-ds1xx2: Don't assume valid sdi
rigol-ds1xx2: fix bitrot in device cleanup code
probe_groups: API changes required to implement probe groups.
Add SR_ERR_PROBE_GROUP, denoting a probe group requirement
rigol-ds1xx2: Minor coding style fixes
rigol-ds1xx2: Better error reporting when probe groups are required
rigol-ds1xx2: Unbreak listing of SR_CONF_DEVICE_OPTIONS
rigol-ds1xx2: Unbreak listing of _VDIV and _COUPLING