transform: remove extra parenthesis to fp8ToI().
transform: unsigned char → uint8_t.
transform: make interpolation source constant.
transform: fix linesize/width confusion.

linesize can be >= to the width; typically within FFmpeg context, the
filter can use the padding between linesize and width for various
purposes (skip fields for interlaced, overlay another frame in the
padded area, ...).

Signed-off-by: Clément Bœsch <clement@stupeflix.com>
defines: simplify PIXEL() and PIXELN()
Merge pull request #10 from ubitux/linesize-width

Linesize width cleanups