added pocketsphinx as an always-on recognizer for 'computer,' activated ...

...using the '-c' command line argument.

The '-c' command line argument stands for continuous: if 'python listen.py -c' is run, Pi-Voice starts the pocketsphinx subprocess to listen for the word 'computer.' Upon hearing the activation word, Pi-Voice will run the listen() function. If the '-c' argument is omitted, Pi-Voice will just run the listen() function immediately and then exit.

This change requires pocketsphinx. I think the only packages necessary are python-pocketsphinx and python-sphinxbase (which I installed on ubuntu using synaptic package manager), but I have not fully tested if this is true. Here is a full list of packages I have installed relating to pocketsphinx:
* libsphinxbase1
* libpocketsphinx1
* pocketsphinx-utils
* pocketsphinx-lm-wsj
* pocketsphinx-hmm-wsj1
To test pocketsphinx installation, you can run pocketsphinx_continuous in the terminal. Let me know if you have any questions!

Thomas