BRLTTY speech driver for "GEnericSay"

This driver is intended to be used with any speech synthesis program
like the rsynth package.

This is preliminary code, still experimental.  Need improovements...

From the perspective of brltty: The command "/usr/local/bin/say" is
invoked with no arguments, and each text string which is to be spoken is
written to the standard input of that command. A period and a new-line (in
that order), i.e. ".\n", are appended to each text string as this is a
reasonably standard way to instruct a speech synthesizer to start speaking
right away. When the speech is to be stopped, i.e. interrupted and
flushed, then the standard input of the command is closed. The command is
restarted the next time there is something else to speak.

From the perspective of the command which must be supplied by the user: It
must be called "/usr/local/bin/say". It is invoked without any arguments.
It must first send any required initialization sequences, and then copy
its standard input, to the speech synthesizer. Upon detecting end-of-file
on its standard input, it should send the "shut up" sequence, followed by
any required shut down sequences, to the synthesizer.

The subdirectory "commands" of this directory contains examples of
"/usr/local/bin/say" scripts for various speech synthesizers.