terminology: add support for some more file extension.

The way to detect image is not that great in fact. Wondering if we
could improve it. Those new type are quite slow btw.

src/bin/extns.h

@@ -4,7 +4,7 @@ static const char *extn_img[] =
    ".bmp", ".ico", ".ppm", ".pgm", ".pbm", ".pnm", ".xpm", ".psd", ".wbmp",
    ".cur", ".xcf", ".xcf.gz", ".arw", ".cr2", ".crw", ".dcr", ".dng", ".k25",
    ".kdc", ".erf", ".mrw", ".nef", ".nrf", ".nrw", ".orf", ".raw", ".rw2",
-   ".pef", ".raf", ".sr2", ".srf", ".x3f", ".webp", 
+   ".pef", ".raf", ".sr2", ".srf", ".x3f", ".webp", ".ppt", ".pptx", ".odp",
    NULL
 };