Also change SIFlaot to pass through 'None'

This solves the issue that not in all cases the
value of 0 can understood as 'not set'.

added in const parsing. Each constant is read processed and added to the kat.constants dictionary. The key is the name of the constant and the value is a namedtuple containing the value and a list of all the lines that reference the constant. Once a constant has been read it replaces the value in any string it finds, so once the command has been parsed you can not change the value of the constant and expect it to change the value of the previously parsed parameters

adding in fsig command (not parsing yet). See example test_fsig.py in bin folder. Also made component variable an optional argument for xaxis and x2axis which will break previous scripts. Did this as when setting the parameter to tune, the Param object contains whatever component owns that parameter so no need to pass it twice. Also stops someone passing a parameter not for the component stated.

adding in fsig command (not parsing yet). See example test_fsig.py in bin folder. Also made component variable an optional argument for xaxis and x2axis which will break previous scripts. Did this as when setting the parameter to tune, the Param object contains whatever component owns that parameter so no need to pass it twice. Also stops someone passing a parameter not for the component stated.

adding in output selection support when noxaxis command is present, can end up with a 0-D array if one output and noxaxis is used, which is odd..

Only thing missing really is the arxiv link to the document.

wz -> w for gaussian parameters.

an error I would prefer to just print that and exit(1).