added support for GCODE commands:

[thatjoshguy]

I have added in the missing support for GCODEs M201, M203, M204, and M205:

• M201 - Set max acceleration in units/s^2 for print moves (M201 X1000 Y1000 Z1000 E10)
• M203 - Set maximum feed rate that your machine can sustain (M203 X200 Y200 Z300 E100) in mm/sec
• M204 - Set default acceleration: P for Printing moves, R for Retract only (no X, Y, Z) moves, and T for Travel (non printing) moves (Not yet implemented) in mm/sec^2 (ex. M204 P800 T3000 R9000)
• M205 - advanced settings: S=printing minimum feed rate, T=travel minimum feed rate, B=minimum segment time, X= maximum x jerk, Y= maximum y jerk, Z=maximum Z jerk, E=maximum E jerk

I added variable travel_acceleration to setting.h but it is not yet being used in motion planning. This setting would affect acceleration on X and Y axis (possibly Z) for travel only moves (when not extruding). We will need to decide how this is handled, as many slicers only use G1 command for all moves vs. G1 for print moves and G0 for travel. This may not be necessary at all.

[thatjoshguy]

note: I removed the "store settings" function from your original functions as these settings should only be stored to EEPROM when M500 GCODE is sent.

[Geeetech3D]

@thatjoshguy Thx! we'll review your code in a few hours