v1.1b: Tweaked Bf reports, jogging doc, saved another 160 bytes, minor bug fixes

- Increment to v1.1b due to status report tweak.

- Tweaked the buffer state status reports to show bytes and blocks
available, rather than in use. This does not require knowing the buffer
sizes beforehand. It’s implicit.

- Also, since buffer states are not used by most devs (after
inquiries), it is no longer enabled by default and a status mask option
was added for this.

- Fixed some typos and updated for the report tweak in the
documentation.

- Wrote a joystick implementation concept in the jogging markdown
document. Outlines how to get a low-latency feel to a joystick (and
other input devices).

- Removed XON/XOFF support. It’s not used by anyone because of its
inherent problems. Remains in older versions for reference.

- Added a compile option on how to handle the probe position during a
check mode.

- Fixed a jogging bug. If G93 is the modal state before a jogging
motion, the feed rate did not get calculated correctly. Fixed the issue.

- Refactored some code to save another 160+ bytes. Included an improved
float vector comparison macro and reducing a few large and repetitive
function calls.

- Fixed a probing bug (existing in v0.9 too) where the target positions
were not set correct and error handling was improper.

doc/markdown/interface.md

@@ -11,11 +11,11 @@ In other words, both commands sent to Grbl and messages received from Grbl have
 
 #### Start Up Message
 
-**`Grbl vX.Xx ['$' for help]`**
+**`Grbl X.Xx ['$' for help]`**
 
 The start up message always prints upon startup and after a reset. Whenever you see this message, this also means that Grbl has completed re-initializing all its systems, so everything starts out the same every time you use Grbl.
 
-* `vX.Xx` indicates the major version number, followed by a minor version letter. The major version number indicates the general release, while the letter simply indicates a feature update or addition from the preceding minor version letter.
+* `X.Xx` indicates the major version number, followed by a minor version letter. The major version number indicates the general release, while the letter simply indicates a feature update or addition from the preceding minor version letter.
 * Bug fix revisions are tracked by the build info version number, printed when an `$I` command is sent. These revisions don't update the version number and are given by date revised in year, month, and day, like so `20160820`.
 
 #### Grbl `$` Help Message
@@ -423,11 +423,19 @@ Feedback messages provide non-critical information on what Grbl is doing, what i
 
     - **Buffer State:**
 
-        - `Bf:0,0`. The first value is planner blocks in use and the second is RX bytes in use.
+        - `Bf:15,128`. The first value is the number of available blocks in the planner buffer and the second is number of available bytes in the serial RX buffer.
+        
+        - The usage of this data is generally for debugging an interface, but is known to be used to control some GUI-specific tasks. While this is disabled by default, GUIs should expect this data field to appear, but they may ignore it, if desired.
+        
+        - NOTE: The buffer state values changed from showing "in-use" blocks or bytes to "available". This change does not require the GUI knowing how many block/bytes Grbl has been compiled with.
 
+        - This data field appears:
+        
+          - In every status report when enabled. It is disabled in the settings mask by default.
+        
         - This data field will not appear if:
 
-          - It is disabled by the `$` status report mask setting.
+          - It is disabled by the `$` status report mask setting or disabled in the config.h file.
 
     - **Line Number:**
 
@@ -547,7 +555,7 @@ Grbl v1.1's interface protocol has been tweaked in the attempt to make GUI devel
 
 - `< >` : Enclosed chevrons contains status report data.
 
-- `Grbl vX.Xx ['$' for help]` : Welcome message indicates initialization.
+- `Grbl X.Xx ['$' for help]` : Welcome message indicates initialization.
 
 - `ALARM:x` : Indicates an alarm has been thrown. Grbl is now in an alarm state.