Additional build info in the $I printout.

- [new] Added total available planner buffer blocks (15 shown, but
there are 16. one is used by the ring buffer and to execute system
motions) and serial RX buffer bytes. This information is useful for
GUIs to setup and optimize their streaming protocols easily.

[doc] Updated the interface document to reflect the change.

doc/log/commit_log_v1.1.txt

@@ -1,3 +1,16 @@
+----------------
+Date: 2017-01-29
+Author: Sonny Jeon
+Subject: Tidying up parking override control implementation
+
+[new] Added a default configuration for the parking override control
+upon a reset or power-up. By default, parking is enabled, but this may
+be disabled via a config.h option.
+
+[fix] Parking override control should be checking if the command word
+is passed, rather than the value.
+
+
 ----------------
 Date: 2017-01-28
 Author: chamnit