Define fringe bitmap BITMAP from BITS of size HEIGHT x WIDTH.
BITMAP is a symbol identifying the new fringe bitmap.
BITS is either a string or a vector of integers.
HEIGHT is height of bitmap. If HEIGHT is nil, use length of BITS.
WIDTH must be an integer between 1 and 16, or nil which defaults to 8.
Optional fifth arg ALIGN may be one of `top', `center', or `bottom',
indicating the positioning of the bitmap relative to the rows where it
is used; the default is to center the bitmap. Fifth arg may also be a
list (ALIGN PERIODIC) where PERIODIC non-nil specifies that the bitmap
should be repeated.
If BITMAP already exists, the existing definition is replaced.
(fn BITMAP BITS &optional HEIGHT WIDTH ALIGN)