Add some monitor mode improvements.

Add some monitor mode improvements.

Added an option to pause and resume the script while running to
allow the user to review the output. Previously, a synthetic probe
was being displayed in the probe list, this is now removed.

* elaborate.cxx:
  - monitor_mode_write: skip generating probe point
    condition for synthetic probes. Add command to resume
    and pause all probes.
  - semantic_pass: call monitor_mode_{read, write} in init
* staprun/monitor.c: Bind keys for pause and resume.