avilib: a pedestrian AVI creator wrapper

AVILIB is a simple wrapper for ML's basic AVI engine to easily create AVI movies using the more
familiar low-level file-i/o syntax of the form:

- aopen : open an AVI file
- awrite : write to an AVI file
- aclose : close an AVI file

takes image(s) of the form
- RGB (x/y/3)
- INDEXED (x/y)
- getframe(...)

performs extensive error checking on subsequent input(s)
- size
- bit-depth

for further explanations see:
help aopen
help awrite
help aclose
help avilib

EXAMPLES
aid=aopen('-f','foo');
for i=1:10
aid=awrite(aid,rand(128,128,3));
aid=awrite(aid,{rand(128,128,3);rand(128,128,3)});
end
aid=aclose(aid);
% if used in a wintel (2k/xp) env
% with <windows player> installed,
% this will show the movie right away:
!foo.avi

set(gcf,'position',[100 100 200 200]);
cm=summer(10);
lh=plot(0:20,rand(1,21),'linewidth',5);
aid=aopen('-f','goo');
for i=1:10
set(lh,'color',cm(i,:));
f=getframe(gca);
r=uint8(255*rand(size(f.cdata)));
aid=awrite(aid,f,r,{f r;f r});
end
aid=aclose(aid);
% !goo.avi