2.05.1.1-simple_dynamic_unretraction 2020-03-29b1

Changes:

• The averaging duration is now configurable: M207 D[seconds]. Default: 0.25
• Improve averaging reliability; fix potential computation errors.
• Fixed the underruns; runs smoother.
• Expanded debug output; it is now possible to validate computations by hand, if needed.

USB debug output:

• regular print move: print [X Y Z] ...
• unretraction move: unretract [X Y Z] ...
• moves that are evaluated prior to unretraction: prepared [X Y Z] ...

Abbreviations in debug output:

• mt: move time
• rate: extrusion rate
• ner: computed next extrusion rate
• ler: computed previous extrusion rate
• ep: extrusion pending (step remainder for very small moves)
• up: computed unretraction compensation
• nc: move count that were used when computing next extrusion rate