#65 Provide proper split screen diff

[Anonymous]

When viewing diffs in two columns, both columns rarely fit on the screen at the same time. Scrolling horizontally to view the content of the right column hides the left column.

Thus, a proper split screen mode is needed, where the screen is split exactly down the middle with one column on each side, and one horizontal scrollbar scrolls both halfs at the same time (e.g. as in Beyond Compare).