Refactor some code out into other module files.

The abstraction is still leaky, certainly, since this really is essentially an overgrown shell script expressed in python; that's not going to change as long as this tool is based on pbs (and in turn pbs's carefree usage of cwd doesn't make things any easier).  Still, this is a half step cleaner.
Update pbs submodule to the present head of development (which includes a renaming; I'm changing the submodule url of course, and references to the files within it, but I'm leaving the submodule's local location unaltered).
Changing command names so that there's only one layer of subcommands instead of there being a whole separate hierarchy under `mdm depend`, because that just felt redunant.  Pushing version number to 1.0.0, because this has been pretty stable... and also because I intend to start a 2.0 branch momentarily which will function radically differently.
release version 1.0.0
Refactor pbs/sh to live in its own directory in the shipped zipbang.
More code rearrangement, splitting mdm code out into other files now.
Fix one echo in mdma that was still referring to the old command names.
Shift the main function for every subcommand into its own file inside the mdm.cmd module.
Fix a help message that was still referring to the old command names.
create branch "branchwise" to start work on mdm 2.0.  This version of mdm will structure release repositories with judicious use of branches and will use remote tracking branch features instead of the "sneaky repo" paradigm in order to attain selective history transfer.

This version of mdm will abandon backwards compatibility with version 1.x since the release repository structures are so entirely dissimilar.  The command line interface however will remain essentially unchanged.
Not much for changes to the `mdm release-init` command, but we do now want to tag an initial commit for making point releases off of.
Split out imports into categories.
remove an unnecessarily reliance on pbs for silly stuff like __main__.py
mdm.
Fix readme references to subcommands names that were changed a few commits ago.
Make it legal to add a submodule with a relative path; output a warning against it, though.
Add gobs of white space.
Improve some error messages in the `mdm add` command to better explain why the situation is a problem.
Fix a couple bugs introduced back in the big refactors that are off the path tested by mdma.
Add documentation for the getMdmSubmodules function.
Implement `mdm release` for branchwise operation.

The dict of data used to overrule normal git commit metadata to be static for convergence purposes doesn't exactly have a place at the moment anymore, but I have a feeling I'm going to want it again sometime soon, so I'm moving that to the mdm.plumbing file.