avutil: actually install hash.h

This header is designed as a public header (with APIchanges entry and
everything), but it is forgotten to put into the headers to be installed
list.

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
swresample: grammar/capitalization fixes

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>