Added new module.

In future all the functions of 'nodevers.shared'
will be moved to 'nodevers.helper.utils'.
Removed modules.

Removed 'nodevers.install', '.install_helper', '.remove',
'.shared', '.use', '.version' and '.versions'.
Added new module.
Made 'nodevers.helper' a module.
Added modules.

Added modules for all commands.
They just setup subparsers at the moment.
'nodevers.cli' now handles argparsing.

Also it is now used as the entry point
by the setup script.
Removed TODO.md.
Bug fix

There were two "version"s in 'nodevers.command.commands'.
(One of them should have been "versions".)
Minor change