MSOS: trigger setting as command line option
Add option to setup the trigger parameters from the command line:
--trigger 1 ' -230e-3' NEG
3 parameters are expected:
- channel number (int)
- threshold value (float)
- slope (string, NEG or POS)
If the threshold value is negative, one must enclose it in quote and prefix
it with a space: 10e-3
or ' -230e-3'
. If omitted, the space is
interpreted as a program option by the parser, and fails.