Labcomm cleanup (still more to do)

Added dynamic macros and code for dynamic arrays indexed by signature
index.

Somewhat improved error handling in readers.

Changed reader/writer interface to simplify stacking (example will 
be forthcoming).

by referring to liblabcomm.a in liblabcomm.so).

fd_reader/writer more robust: no dependency on 'int *fd' to be live
while the reader/writer is in use).

a writer directly.

labcomm_encoder/labcomm_decoder into labcomm.c

indirection in generated C-code.

Updated wiki_example to use StreamReader.