Realtime rate reporting. Updated decimal places.

- Added a new optional compile-time feature for ‘realtime’ (within
50ms) feed rate reporting. When querying for a status report, a new
data value will state the current operating rate. It’s only beta at the
moment and has some kinks to work out.

- Updated the code for printing floating point values to N decimal
places. Generalized the main floating point print code to accept a new
decimal places value and created a set of handler functions to print
certain floating point value types used in Grbl, like position, rates,
coordinate offsets, etc. All of these have different decimal
requirements and change when printed in mm or inches mode.

- Number of decimal places for the different value types can be
re-defined in config.h, but there shouldn’t be a need for this, as
these are physically limited.

- Removed the decimal places settings, as this was now obsoleted by the
new decimal places code.

- The new decimal places code also saves almost 300kB in flash space,
as it’s more efficient.

config.h

@@ -84,10 +84,26 @@
 // parser state depending on user preferences.
 #define N_STARTUP_LINE 2 // Integer (1-3)
 
-// Allows GRBL to tranck and report gcode line numbers.  Enabling this means that the planning buffer
+// Number of floating decimal points printed by Grbl for certain value types. These settings are 
+// determined by realistic and commonly values observed in CNC machines. For example, position
+// values cannot be less than 0.001mm or 0.0001in, because machines are never more precise than 
+// this. So, there is likely no need to change these, but you can if you need to here.
+// NOTE: Must be an integer value from 0 to ~4. More than 4 may exhibit round-off errors.
+#define N_DECIMAL_COORDVALUE_INCH 4 // Coordinate or position value in inches
+#define N_DECIMAL_COORDVALUE_MM   3 // Coordinate or position value in mm
+#define N_DECIMAL_RATEVALUE_INCH  1 // Rate or velocity value in in/min
+#define N_DECIMAL_RATEVALUE_MM    0 // Rate or velocity value in mm/min
+#define N_DECIMAL_SETTINGVALUE    3 // Decimals for floating point setting values
+
+// Allows GRBL to track and report gcode line numbers.  Enabling this means that the planning buffer
 // goes from 18 or 16 to make room for the additional line number data in the plan_block_t struct
 // #define USE_LINE_NUMBERS // Disabled by default. Uncomment to enable.
 
+// Allows GRBL to report the real-time feed rate.  Enabling this means that GRBL will be reporting more 
+// data with each status update.
+// NOTE: This is experimental and doesn't quite work 100%. Maybe fixed or refactored later.
+// #define REPORT_REALTIME_RATE // Disabled by default. Uncomment to enable.
+ 
 // Enables a second coolant control pin via the mist coolant g-code command M7 on the Arduino Uno
 // analog pin 5. Only use this option if you require a second coolant control pin.
 // NOTE: The M8 flood coolant control pin on analog pin 4 will still be functional regardless.