0. INTRODUCTION
This is a port and cleanup of my bash debugger bashdb
(http://bashdb.sf.net). 

The command syntax generally follows that of the GNU debugger gdb.

However this debugger depends on a number of bug fixes and of debugging
support features that are neither part of the POSIX 1003.1 standard
and only in ksh93t+ releases. In particular, there are fixes to a
number of the .sh variables like .sh.level and .sh.file.

1. SETUP

See https://github.com/rocky/kshdb/wiki/How-to-install for how to install this code. 

2. WHAT'S HERE, WHAT'S NOT and WHY NOT

What's missing falls into two categories:

  * Stuff that can be ported in a straightforward way from bashdb
  * Stuff that needs additional ksh support

Of the things which can be ported in a straight-forward way, however
some of them I want to revise and simplify. In some cases, the fact
that ksh has associative arrays simplifies code. On other cases, the
code I wrote needs refactoring and better modularization.

Writing documentation is important, but an extensive guide will have
to wait. For now one can consult the reference guide that comes with
bashdb: http://bashdb.sf.net/bashdb.html There is some minimal help to
get a list of commands and some help for each.

3. WHAT'S NOT HERE YET IN DETAIL

This can be done with or without support from ksh, albeit faster with
help from ksh.

3.a) Setting $0

3.b) lots of other stuff including...

  display expressions, signal handling, 
  debugger commands:
     debug
     file
     handle
     history
     signal
     tty
     watch

  None of this is rocket science. Should be pretty straight-forward to
  add.

4. WHAT MAY NEED MORE WORK AND SUPPORT FROM KSH

4.a) stopping points that can be used for breakpoint