pub fn parse_file(spec: &str) -> Result<(String, FileDef), String>
Parses NAME=path,KSDS,key=OFFSET:LENGTH,len=RECLEN[,text|,fixed|,variable] or NAME=path,RRDS,len=RECLEN[,text|,fixed|,variable].
NAME=path,KSDS,key=OFFSET:LENGTH,len=RECLEN[,text|,fixed|,variable]
NAME=path,RRDS,len=RECLEN[,text|,fixed|,variable]