Start implementing a new foundation for the ssmount commands.

- Doing this ourself allows us to control usage output and allows us to implement `ssmount help <command>`.
- A command line argument parser has been implemented.
  - Behind the scenes cli-argparse is used in strict mode to parse argv.
  - By using cli-argparse's strict mode along with a bit of positional argument handling our argparse can parse
    some arguments like --version and --help as well as the command, and then leave the rest unparsed
    to be parsed as command-specific arguments.
- Since it's not ready yet the new stuff is being named `ssmount2` until complete.
Implement a version command in ssmount2.
ssmount2: Add add "not a ssmount command" message.
ssmount2: Implement `ssmount list` in the new style commands
ssmount2: Implement add, rm, mount, unmount, ssh, and subl in new style commands.
ssmount2: Implement throw exits.
ssmount2: Implement required arguments.
ssmount2: ssmount -> error
Handle the case where subl isn't available.
ssmount2: Start outputting a basic usage with commands when no args are used.
ssmount2: Implement full usage and help.
Now that it's complete move ssmount2 over ssmount.
Merge branch 'feature/newcommand' into develop
0.3.0
Merge branch 'release/0.3.0' into develop