add code to communicate with common lisp (SBCL) between computer and arduino due
there was a potential bug when ungetc2 gets called just after a new buffer has been acquired
define some functions to access digital analog converter and analog digital converter
added a delay function, now the dac channels can be digitized again
example output:
welcome to femtolisp ----------

> (lambda args args)

> ((t t 0 0) (t t 414 0) (t t 871 0) (t t 0 416) (t t 0 856) (t t 0 0))

> ((t t 0 0) (t t 418 0) (t t 872 0) (t t 0 418) (t t 0 858) (t t 0 0))

> ((t t 0 0) (t t 428 0) (t t 874 0) (t t 0 419) (t t 0 858) (t t 0 0))

>