1) zoom-center :: bool
zoom-center = false
If zoom-center = false nothing changes.
If zoom-center = true zooming respects the horizontal center of the
pageview. That is, the vertical line dividing the displayed part of
the document doesn't move within the document.
Reasoning: When viewing a pdf with a margin we usually want to hide the
margin at both sides by zooming in.
2) scroll-hstep :: float
scroll-hstep = -1
If scroll-hstep < 0 nothing changes.
If scroll-hstep >= 0 then scroll-hstep defines the scroll step in the
horizontal direction.
Reasoning: This allows us to make finer adjustments in the horizontal
direction without the mouse and without loosing the ablility to
navigate quickly through the document.
3) search-hadjust :: bool
search-hadjust = true
If search-hadjust = true nothing changes.
If search-hadjust = false searching does not adjust the horizontal
center of the document when showing search results.
Reasoning: When viewing a pdf with a margin we usually want to hide
the margin at both sides by zooming in. The horizontal adjustment
sometimes hides parts of the document by moving the horizontal
center.
