Is your feature request related to a problem? Please describe.
mas could use a few aliases, to bring it more in line with brew and cask…

Describe the solution you'd like
These could include:

• mas -v/--version -> mas version
• mas -h/--help -> mas help
• mas ls -> mas list
• mas i -> mas install
• mas rm -> mas uninstall
• mas upgrade -> mas update
• mas purchase -> mas install <with arguments> (after install is updated to "purchase")
• mas signin -> mas sign-in
• mas signout -> mas sign-out

REJECTED:

• mas update -> brew upgrade mas