Minor re-factoring. Fix an issue with parking and spindle restore.

- Altered the report counters to be count down, rather than count up.
Simplified some of the logic.

- Fixed an issue with parking restore. The spindle state would disable
then reenable.

- Clarified some of the config.h descriptions.

- Moved the compile-time checks from config.h to grbl.h. They don’t
belong in the config.h file.

- Refactored the initialization of the system variables in main.c.
System position and probe position were undefined when power cycled,
but were zero anyway. Added clear vector code to make it explicit.

doc/log/commit_log_v1.1.txt

@@ -1,3 +1,18 @@
+----------------
+Date: 2016-10-23
+Author: Sonny Jeon
+Subject: Spindle speed close to minimum fix.
+
+- When spindle speed is close to the minimum rpm, the PWM value would
+be zero or lower than allowed. The computation error was caused by
+setting the minimum PWM value to zero, when it should have been 1.
+
+- Added a compiler check for minimum PWM to be greater than zero.
+
+- Moved some of the spindle PWM macros to a more appropriate place in
+the cpu_map.h.
+
+
 ----------------
 Date: 2016-10-22
 Author: Will Winder