COPYING: Add GPLv3 license.

Signed-off-by: Jon Seymour <jon.seymour@gmail.com>
Introduce j.sh, jsh.j.

j.sh is a wrapper script that is linked to from a directory on the PATH.

Each such link represents a command that will invoke the top-level
module of a jsh package.

jsh.j is the top-level module of the jsh package itself.

Signed-off-by: Jon Seymour <jon.seymour@gmail.com>
jsh/module/module.j: introduce support for deriving the module file name from a module specification.

Signed-off-by: Jon Seymour <jon.seymour@gmail.com>
jsh/module/{edit,create}.j: add support for creating and editing jsh modules.
jsh/{help,usage}.j: provide help and usage information for jsh.
README.md: udpate to include BOOTSTRAP information.