Add summary of generating commands to RO file/data structure

[Ian Culverwell]

It would be useful to have a summary of the input commands that were used by an ROPP tool. This should include the various bits of data that are held in configuration files. The best place to hold this might be as a global attribute in the netCDF file. (I can't think of many input options that are profile-specific, and which would therefore need to be held in the ROprof structure.)

For instance, the global attribute

unix> ncdump -h temp.nc

//global attributes:
		:command_summary = "\noutput_tdry = .true.\nocc_method = WO\nfilter_method = slpoly\nfw_go_smooth = 3000.0" ;

would allow the user to tell that the (ropp_pp) tool which generated the file used the parameters

unix> ncks -M temp.nc |tac |head -5 |tac

output_tdry = .true.
occ_method = WO
filter_method = slpoly
fw_go_smooth = 3000.0

We could also include run time, $PWD, input/output file names etc in the command_summary global attribute. Shouldn't be too hard, I think.