[Jprogramming] new api/jc addon

[Eric Iverson]

api/jc is a new addon. It's cleaned up from bits and pieces I found useful
over time and might be of interest.

It provides J bindings for C library routines (streams/fds/system/etc.) and
some simple utils with stdin/stdout.

The cleanup was triggered by discussions in the source forum about 2!:3
crashes. 2!:3 has not worked since at least 602 (possibly never). We will
remove 2!:3 from 807.

api/jc also has a preliminary version of a simple doc system in the spirit
of unix man pages. A quick addon summary that is easy to maintain and
always at your finger tips.

If interested, try:
   load'~addons/api/jc/jc.ijs'
   man''
   man'jc '
   man'jc 4' NB. all platforms - 2!:3 facility that works
try some examples
   man'jc 5' NB. unix only - interactive stdin/stdout facility
try some examples