'keys' does not handle special keys (like ^J) anymore.
Instead, we should use `key`, which will pass its entire
argument to tmux, without any processing. It is therefore
possible to do something like:
```key ^C```
Or
```key Escape```
Most (if not all) calls to special keys have been
converted to use 'key' instead of 'keys'.
Action ```copypaste``` has been deprecated in favor
of three separate actions:
```copy REGEX``` (searches the regex in the active pane,
and if found, places it in an internal clipboard)
```paste``` (inserts the content of the clipboard as
keystrokes)
```check``` (forces a status check)
Also, a 'tmux' command has been added. It allows to
do stuff like:
```tmux split-pane -v```
