patchu.icn: Program to implement UNIX-like patch

This program reads a source file and a diff file, producing an
updated file.  The diff file may be generated by the UNIX diff(1)
utility, or by diffu.icn, which uses dif.icn for the hard work.

The original patch(1) utility, written by Larry Wall, is widely
used in the UNIX community.

The diff file contains edit lines, separators, and text lines.
Edit lines may take the forms:

     #a#[,#]                 <- add    lines
     #[,#]c#[,#]             <- change lines
     #[,#]d#                 <- delete lines

Change lines contain only the string "---".  All other lines are
text lines.  See diff(1) in any UNIX manual for more details.