libjpeg API: Partial scanline decompression

This, in combination with the existing jpeg_skip_scanlines() function,
provides the ability to crop the image both horizontally and vertically
while decompressing (certain restrictions apply-- see libjpeg.txt.)

This also cleans up the documentation of the line skipping feature and
removes the "strip decompression" feature from djpeg, since the new
cropping feature is a superset of it.

Refer to #34 for discussion.

Closes #34

win/jpeg62-memsrcdst.def

@@ -103,3 +103,4 @@ EXPORTS
 	jpeg_mem_dest @ 102 ; 
 	jpeg_mem_src @ 103 ; 
 	jpeg_skip_scanlines @ 104 ; 
+	jpeg_crop_scanline @ 105 ; 

win/jpeg62.def

@@ -101,3 +101,4 @@ EXPORTS
 	jround_up @ 100 ; 
 	jzero_far @ 101 ; 
 	jpeg_skip_scanlines @ 102 ; 
+	jpeg_crop_scanline @ 103 ; 

win/jpeg7.def

@@ -103,3 +103,4 @@ EXPORTS
 	jround_up @ 102 ; 
 	jzero_far @ 103 ; 
 	jpeg_skip_scanlines @ 104 ; 
+	jpeg_crop_scanline @ 105 ; 

win/jpeg8.def

@@ -106,3 +106,4 @@ EXPORTS
 	jround_up @ 105 ; 
 	jzero_far @ 106 ; 
 	jpeg_skip_scanlines @ 107 ; 
+	jpeg_crop_scanline @ 108 ;