#2 Need stretch and alignment fields on BackgroundInline

[Chris Marrin]

Here is a proposal for the IMAGE mode of
BackgroundInline, to allow the image to be displayed
in a variety of ways:

field SFString stretch "SLICE"
field SFString alignment "XMID_YMID"

Possible values for stretch are:

"NONE" - the image is drawn pixel-perfect, with no scaling.

"FIT" - the image is scaled in x and y to match the
size of the client surface, without preserving the
aspect ratio of the image.

"MEET" - the image is scaled so that its entire surface
is visible and it fills one dimension of the client
surface completely. The aspect ratio is preserved.

"SLICE" - the image is scaled so that it fills the
entire client surface and it exactly fits one dimension
of the client surface. The aspect ratio is preserved.

Possible values for alignment are:

"XMIN_YMAX", "XMID_YMAX","XMAX_YMAX",
"XMIN_YMID","XMID_YMID","XMAX_YMID",
"XMIN_YMIN","XMID_YMIN", and "XMAX_YMIN"

This aligns the left (XMIN), center (XMID) or right
(XMAX) edge of the image horizontally and the bottom
(YMIN), center (YMID), or top (YMAX) edge of the image
vertically.