Change split, focus, close, activate window, select tab, close tab, and
close window commands to accept their target object as a direct parameter
instead of a named parameter. This produces natural AppleScript syntax:
activate window (window 1)
close tab (tab 1 of window 1)
split (terminal 1) direction right
instead of the awkward redundant form:
activate window window (window 1)
close tab tab (tab 1 of window 1)
split terminal (terminal 1) direction right
The implementation moves command logic from NSScriptCommand subclasses
into responds-to handler methods on ScriptTerminal, ScriptWindow, and
ScriptTab, which is the standard Cocoa Scripting pattern for commands
whose direct parameter is an application class.
Add a new `split` command to the AppleScript scripting dictionary that
splits a terminal in a given direction (right, left, down, up) and
returns the newly created terminal.
The command is exposed as:
split terminal <terminal> direction <direction>
Also adds a `fourCharCode` String extension for converting four-character
ASCII strings to their FourCharCode (UInt32) representation.
