[Bug-apl] Packager updated for GNU APL 1.6

[David B. Lamkins]

With the release of GNU APL 1.6, I thought that this would be a good time to 
update the APL Package Manager.

https://github.com/TieDyedDevil/apl-pkg

The big change here is that the development branch (percy) has been merged onto 
master. There are a lot of new features (see below). There won't be a tagged 
release; I strongly suggest that you clone the git repo and pull updates 
periodically.

This remains a development release since the primary feature of the percy 
release (i.e. versioned packages) is not fully implemented. This won't affect 
you; just don't try to add version constraints to the depends_on: entries in 
your _metadata_ files.

Note that akt has been updated since the last release. It is essential that you 
re-run `./install.sh` to rebuild akt, or run `$ make -C extra/akt`.

There have been a lot of changes since the last release. From the 
doc/CHANGES.md file:

Features
--------

- The `]pkg inspect <variable-name>` command runs an interactive inspector.
  The inspector shows attributes of the variable and provides commands to
  navigate through the data. Use the inspector's `h` command to list available
  commands.

- The `]pkg time <expression>` command executes the expression and displays
  its execution time.

- The `]pkg ident platform` command displays information about the platform
  upon which the package manager runs.

- The `]pkg ident environment` command displays information about the
  runtime environment.

- The `]pkg ident configuration` command displays the APL Packager's
  configuration settings.

- The `]pkg setpw` command updates ⎕PW to match the detected terminal width.

- The `]pkg locate <function-name> header` command displays the function's
  information plus its header line and header comments (i.e. all of the
  full-line comments immediately following the header line, up to the first
  line that's not a comment).

- The `]pkg help` command's display brackets metasyntactic variables to
  distinguish them from literal keywords.

- The `]pkg names <prefix>` command rejects an invalid prefix.

- The `]pkg packages` command displays a legend for the flags in the `L`
  column.

- The `awe` command confirms that `apl.pkg` in APL's LIB 0 is a symlink.
  This is a check against both inadvertent removal and replacement by a
  file (e.g. a )DUMP file).

- The `awe` command invokes `tabbed` when available. This is done only when
  running under X, when the configured terminal is known to `awe`'s built-in
  list (`xterm`, `urxvt` and `st`) and `awe` is not invoked from within an
  Xembed container. See `doc/PREFERENCES.md` for a description of settings
  which affect embedding.

- The `awe` commands accepts option `-i #` to set the shared variable
  processor ID.

- Displays now wrap at the terminal's actual width if the `tput` command
  is available.

- The command dispatcher now displays a usage message, rather than a list
  of all commands and their syntax, for an ill-formed command.

- The command dispatcher now displays a list of commands having a matching
  prefix when presented with an ambiguous prefix.