added missing `sign` argument for apksigner

See discussion in #933.

See discussion in #933.

using sox for ssml <audio> tag is hardcoded in readclause.c and for
--compile-phonemes in compiledict.c

Currently, --compile-phoneme doesn't need to run sox since the
samplerate for the specific file is correct. There might be a lot of
dead code in compiledata.c

Current link points to docs/docs/add_language.md (because we are already in docs). Duplicated docs is removed.

Literally following the instructions on a base install of Debian results in a build without audio support. This change adds the instruction for installing pcaudiolib development headers, so that the resulting build has audio.

- use open source key storage (PKCS 12)
- update location of target files