Restructure code.

   This is quite a bit in one commit but it:

       * Splits the app into an app and module so the analysis components
         can be re-used. Also tidied up all the header files in the app.
       * Updates the app_handler to syphon off i2s samples (renamed to i2s_tap)
       * Changes the communication between the i2s tap and the analyzer
         slightly
       * Updates to be able to test based on i2s loopback

   Currently the code only works in simulation (axe command line added to
   Makefile)
Merge branch 'master' into d
Merge pull request #1 from davelxmos/d

Some code restructuring