Integrate accessors.h header into internal.h

I have no idea why I added a separate header,
I think there is no good reason for it.

Signed-off-by: Reimar Döffinger <Reimar.Doeffinger@gmx.de>
doc: apply various grammar fixes

The first sentence of each of the modified man pages are worded a bit
awkwardly. These minor copy-edits should make them clearer.

Signed-off-by: Bryce Harrington <b.harrington@samsung.com>
Signed-off-by: Stefano Sabatini <stefasab@gmail.com>
doc/filters: fix sine sample_rate abbreviation

Signed-off-by: Stefano Sabatini <stefasab@gmail.com>