6CYANA: write prot - CYANA command

Parameters: file=<filename>.prot           (required)
            list=<integer>                 (default: 1)
            nmrstar=<integer>              (default: 2)
            details
            multiple
            append

Write a chemical shift list (traditionally called "proton list") in
Xeasy format (Eccles et al., 1991; Bartels et al., 1995). Optionally,
the output may be appended to an existing file.
