TODO
- add local variable support that can be interpolated into commands
- keep track of previous command outputs for last command, and any previous command with target list and command line
  - Allow any given command to be tagged with a label, and the outputs would be stored in the output dictionary under that name (for scripting);
    we assign a default name to it, and are able to refer to it based on either the label, or how many commands back it was;
  - scripts entire output is stored as one label, but also
  - add commands to show the list of captured outputs, along with the commands and targets
  - add commands to search captured outputs
  - add commands to search captured outputs and put them into a variable that can be used for /target etc.
- calling commands and aliases from command line (e.g. multiball -t <targets> -c <command>)
- tagging and filtering commands (so `noupgrade` gets a tag, and we can filter them)
- saving the last host set in a .file
- allow server groups / server labels
- add 'watch' to run a command repeatedly until it succeeds (interruptable)
- add the number of servers for each group of services too
- notice when you don't sudo in front of command and it errors and ask you if you meant to sudo
- autocomplete for environment variable names (requires heirarchical completer)
- implement target aliases (-filteralias) which gives a label to an argument to -hosts
- ad-hoc host groupings with assigned names, and a host grouping stack
- allow scripts that use -safe to prompt for safety / restore safety after running
- implement various commented commands in the command list
- implement interactive alias system
- Catch more exceptions in fabtools, and also add retries
- Make the runner aware of multiple commands so that it can combine outputs and make 'overall success' or 'overall failure'
- make C-c break the connections not the program
- make a /summary command that *only* outputs the summary of a remote command, not the stdout/stderr