Makefile: make "tg help help" work

The help for help is there it just has to be included in
the list of help commands so it gets built.

Signed-off-by: Kyle J. McKay <mackyle@gmail.com>
tg: add support for tg help -w command

Like git, tg help -w command will attempt to open documentation
for the specified command in a web browser.

Requires rst2html.py at build time and then running the commands
"gmake html" and "gmake install-html" to build and install it.

Uses git's web--browse command to open the help in a browser.

Signed-off-by: Kyle J. McKay <mackyle@gmail.com>
Makefile: add some helpful rules for non-GNU makers

Add a comment and helpful rules that cause most non-GNU
make commands to bail out early with a helpful error.

If running with GNU make the helpful additions do nothing.

Signed-off-by: Kyle J. McKay <mackyle@gmail.com>
Set version to 0.12

Signed-off-by: Kyle J. McKay <mackyle@gmail.com>
docs: minor updates including a source repository link

Signed-off-by: Kyle J. McKay <mackyle@gmail.com>