Add trace_readline_fields helper to parse the output of trace_pipe
Add field parsing support to trace_print. Addresses #149.
Fix typo in trace_open s/trace/tracefile/
Make nonblocking=False the default in trace_readline
Use IOError vs BlockingIOError for greater compatibility (untested)

Fixes: #149
Signed-off-by: Brenden Blanco <bblanco@plumgrid.com>