Position reporting, refactored system variables, serial print fixes, updated streaming scripts.

- Added machine position reporting to status queries. This will be
further developed with part positioning/offsets and maintaining
location upon reset.

- System variables refactored into a global struct for better
readability.

- Removed old obsolete Ruby streaming scripts. These were no longer
compatible. Updated Python streaming scripts.

- Fixed printFloat() and other printing functions.

- Decreased planner buffer back to 18 blocks and increased TX serial
buffer to 64 bytes. Need the memory space for future developments.

- Begun adding run-time modes to grbl, where block delete toggle, mm/in
reporting modes, jog modes, etc can be set during runtime. Will be
fleshed out and placed into EEPROM when everything is added.

script/simple_stream.py

@@ -1,6 +1,15 @@
 #!/usr/bin/env python
 """\
 Simple g-code streaming script for grbl
+
+Provided as an illustration of the basic communication interface
+for grbl. When grbl has finished parsing the g-code block, it will
+return an 'ok' or 'error' response. When the planner buffer is full,
+grbl will not send a response until the planner buffer clears space.
+
+G02/03 arcs are special exceptions, where they inject short line 
+segments directly into the planner. So there may not be a response 
+from grbl for the duration of the arc.
 """
 
 import serial