Plug-in & configuration system enhancements

[curlpipe]

• Default plug-ins that are always enabled regardless of user's system
• Rename to space in key bindings (but allow as well)
• Better document type in status line (to prevent it being empty)
• Configurable help message and smaller greeting message by default (#147)
• Allow more substitution options on help message and greeting message
• Better plug-in and configuration errors
  • better errors being fed to main.rs
  • scan through editor API calls and see if there is a way to fire an error there
  • try different things to see if all errors are reported appropriately
• Plug-in management system (installing, removing, checking the status of)
• More advanced plug-in API
  • Allow binding to events before the editor applies the changes based on that key press
  • Networking (HTTP get requests)
  • Request re-rendering of certain parts of the editor
  • Have a system like "run function f every n seconds"
  • Can render plug-in output in certain areas
    • greeting message
    • help message

[curlpipe]

Completed with the release of 0.6.3