feat: add clear and exec command

nature/commands/clear.lua

@@ -0,0 +1,7 @@
+local ansikit = require 'ansikit'
+local commander = require 'commander'
+
+commander.register('clear', function()
+	ansikit.clear(true)
+	ansikit.cursorTo(0, 0)
+end)

nature/commands/exec.lua

@@ -0,0 +1,5 @@
+local commander = require 'commander'
+
+commander.register('exec', function(args)
+	hilbish.exec(args[1])
+end)