move from legacy precise to trusty build image
fix PATH not including buildroot/bin
remove symolic link to ~/bin
enable sudo

trusty travis image doesn't source ~/bin by default
avr requires sude

TravisCI "trusty" build dist isn't picking up build path causing travis checks to fail.  Reverting to legacy "precise" dist while we investigate

pristine != precise

Clarify LCD_BED_LEVELING requirements

Fix for #7395

LCD_BED_LEVELING requires PROBE_MANUALLY with auto bed leveling enabled.  See #7396

Filament change causes freeze during paused print. This PR disables Filament change in the prepare menu when a print from SD Card is paused. See #7395

Fix DUAL_X_CARRIAGE movement

Axis would only move when homing.
Bug introduced in 91841d75c9.
Fixes #6956, fixes #7050 and fixes #7291

Manual Bed Leveling: Goto previous Z height at each probe point

Implement probing delay for piezo sensors

Fixes for FWRETRACT

Move Delta Calibration menu to the Prepare menu

Patch to fix some compiler warnings

Makefile fixes and U8G support.

Add X_BED_SIZE, Y_BED_SIZE to configurations

Add PIO entry for PRINTRBOARD_REVF

Remove extraneous USBCON defines for AT90USB boards

fix from PIO corruption

USBCON is definied by serial.h pullikng in MarlinConfig.h which in turn pulls in Arduino.h.  Defining in later includes has shown to cause compile issues so removing all extraneous calls for and potentially easier future linker troubleshooting.
more USBCON unification

Add support for Printrbot Neopixel RGBW strip.

Connected as described at http://printrbot.com/shop/led-strip/

Based on patch by Kelly Anderson <kelly@xilka.com> at
http://www.xilka.com/printrbot/marlin/1.1.4/20170707/

MKS 1.3+: Add pin mapping for PS_ON

Update Russian translation - Part 1

Signed-off-by: Alexey Shvetsov <alexxy@gentoo.org>

Fixing SWITCHING_EXTRUDER feature to work with HOTENDS > 1

This allows the use of D4 as PS_ON since MKS Gen doesn't have a PS_ON pin. However this effectively allows only 3 servos (instead of 4).

Signed-off-by: Alexey Shvetsov <alexxy@gentoo.org>

Improve FWRETRACT comments

Add more details as requested in #7198