Add a postprocessing hook: for creation of the WAV file, add a "hook" so that the user can also run e.g. lame to create MP3

[Wikinaut]

I wish to be able to add permanently a post-processor command (pipe) like
`lame -h -V2 - "filename.mp3"``

In the above example the - takes the output from gespeaker as input to lame, and filename stems from the user record filename selection step.

As an alternative automatically call lame when the user selected "mp3" as filename extension (instead of "wav", which is the currently only choice.