Add assert to try to find crash
Don't free null run
Fix bug where the char under the cursor wasn't drawn
Add DECLRMM(DECVSSM; vertical split-screen mode)
Add left/right margin
Apply left/right margin with NL/SU/SD/IND/RI

Conflicts:
	VT100Screen.m
Apply left/right margin with IL/DL
Reset left-right scroll margin when reset/resized
Reset vertical screen split mode with RIS
Apply L/R margin only when DECSCLM is enabled
Treat vscroll mode as screen property
Apply L/R margin to HUP/HVP
Allocate appropriate amount of cells when scrolling
Respect left margin on carriage return
fix-for new line
setString(+autowrap mode/insert mode) respects left-right margin
Respect left-right margin when BS is invoked
CUB/CUF should respect L/R margins
The default value of DECSCRM is (1, width)
Respect DECOM and L/R margins when CHA is invoked