swresample: allow double precision beta value for the Kaiser window

Kaiser windows inherently don't require beta to be an integer. This was
an arbitrary restriction. Moreover, soxr does not require it, and in
fact often estimates beta to a non-integral value.

Thus, this patch allows greater flexibility for swresample clients.
Micro version is updated.

Reviewed-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@gmail.com>

doc/resampler.texi

@@ -220,7 +220,7 @@ select Kaiser windowed sinc
 @end table
 
 @item kaiser_beta
-For swr only, set Kaiser window beta value. Must be an integer in the
+For swr only, set Kaiser window beta value. Must be a double float value in the
 interval [2,16], default value is 9.
 
 @item output_sample_bits