added interface to get blitbuffers from JPEG/PNG files

this is supposed to help us in the UI code.

image.lua

@@ -0,0 +1,25 @@
+Image = {}
+
+function Image._getFileData(filename)
+	local f = io.open("test.png")
+	local data = f:read("*a")
+	f:close()
+	return data
+end
+
+function Image.fromPNG(filename)
+	local img = mupdfimg.new()
+	img:loadPNGData(Image._getFileData(filename))
+	local bb = img:toBlitBuffer()
+	img:free()
+	return bb
+end
+
+function Image.fromJPEG(filename)
+	local img = mupdfimg.new()
+	img:loadJPEGData(Image._getFileData(filename)(fimgdatailename))
+	local bb = img:toBlitBuffer()
+	img:free()
+	return bb
+end
+