ddPrint - Adding Process control to FDM printers

* Merged the avr changes into master branch.

* New branch *next* is where current development ist taking place, cleanup and other small improvements.

* Recording some asciinema screencasts to show usage of ddprint commands.

Pushed a new firmware branch *fix-avr* to github. The JennyPrinter port made the avr/atmega side to slow.

Changes are:

* Integer math instead of floating point.
* Reworked usb-serial interface: store 512byte blocks.
* Removed compression with zlib, the avr has not enough cpu cycles.
* Experiment: auto-baudrate. Switch between 1000000, 500000 and 250000 baud.
* SDReader: double-buffering.
* Many other improvements and cleanup.

So for now, fix-avr is the branch to use for avr/atmega based printers and master is for
the stm32 JennyPrinter. Branch fix-avr has will be merged into master.

Merged *next branch* into master with the following changes:

* Feed forward temp control (*PID hinting*, *guided PID*) :-o
  AutoTemp algorithm: set new temperature some time before the new flowrate demand, 
  using the information from the material profile.
* Added a experimental gcode (M901) for part strength (along with new *workingpoint*
  command line parameter) :-o
* Asymmetric PID temperature control: switch between different PID control sets for
  heating (fast) and cooling (a slower PID set to avoid temperature underruns).
* Deflate/zip data downloaded to printer to increase download speed over usb-serial.
  Using python's zlib on the host and uzlib (https://github.com/pfalcon/uzlib) on
  the firmware side.
* Added a second step to material profile measurement (measuretempflowratecurve2):
  Measure hotend performance while doing a real print, in addition to the *into-the-air*
  extrusion measurement.
* Some smaller improvements:
   + Moved printer-, nozzle- and material-profiles into their own
     repository (https://github.com/ErwinRieger/ddprint-profiles).
   + Show print time in CLI and terminal UI (TUI).
   + Show the number of *under-temperature* and *under-grip* warnings in TUI.
   + Added a *printlog* to ddprintui.py: log information about the current
     printjob (gcode info, timestamp, printing time, slicersettings).
   + Added some tools and scripts (plot_mat_profile, ddtool, wrapperscripts).
   + Removed usage of eeprom, configuration now stored on mass storage device (sdcard, usb).
   + And many more...