Open you user keys file .sublime-keymap
and add this:
{
"keys": ["alt+shift+1"],
"command": "set_layout",
"args":
{
"cols": [0.0, 1.0],
"rows": [0.0, 1.0],
"cells": [[0, 0, 1, 1]]
}
},
{
"keys": ["alt+shift+2"],
"command": "set_layout",
"args":
{
"cols": [0.0, 0.5, 1.0],
"rows": [0.0, 1.0],
"cells": [[0, 0, 1, 1], [1, 0, 2, 1]]
}
},