Adds the inspector commands to lispkit

Keybinds:

- C-x-i-o: opens inspector
- C-x-i-c: closes inspector
- C-x-i-a: attaches inspector
- C-x-i-d: detaches inspector

C-x-i was chosen because "inspector".
Add toggling for the inspector
Always set the enable-developer-extras slot-value to t.

No premature optimization.
Merge pull request #45 from Ralt/inspector

Adds the inspector commands to lispkit