Use CmdArgs for Command & Argument Parsing

* Add a Main.CLI module to hold the CLI dispatch and command mode
  functions and types.
* Add help, command and completion information to the README.

* Replace custom commandHandler and printUsage functions with CmdArgs
  argument parsing.

* Move the Redmine Actions from the Main module to the Main.Actions
  module.
* Move the CLI parsing and dispatch functions from the Main module to
  the Main.CLI module.