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.

doc/log/commit_log_v1.1.txt

@@ -1,3 +1,47 @@
+----------------
+Date: 2016-10-22
+Author: Will Winder
+Subject: Minor VARIABLE_SPINDLE feature toggle refactoring (#16)
+
+* Modify code CSV format.
+
+- Wrap value in quotes to avoid issue with embedded commas. This occurs
+  in one of the alarm codes.
+
+- Change header row format to allow same parsing code as data rows.
+
+* VARIABLE_SPINDLE feature flag experiment.
+
+- Use a macro for 'spindle_set_speed' and 'spindle_sync' to reduce the
+  number of required VARIABLE_SPINDLE checks.
+
+
+----------------
+Date: 2016-10-18
+Author: Sonny Jeon
+Subject: Improved option for v0.9 GUI compatibility.
+
+- Addressed an issue with backward compatibility with Grbl v0.9-style
+GUIs.
+
+- It still may not work due to new data and states coming back from
+Grbl v1.1. Regardless, DO NOT TRY TO USE THE COMPATIBILITY MODE UNTIL
+THERE IS A REALLY GOOD REASON TO.
+
+- v0.9 GUI compatibility mode will be removed in future versions.
+You’ve been warned. It’s highly recommended for GUIs to update to the
+new v1.1 interface.
+
+- Compability mode will only fit on an Arduino Uno due to size
+increases.
+
+- Removed the REPORT_GUI_MODE compile option since it’s part of the
+v1.1 interface standard.
+
+- Updated the documentation to better describe the compatibility mode
+build option.
+
+
 ----------------
 Date: 2016-10-17
 Author: Sonny Jeon