Release firmware v1.9.x/"2.0"

[Ultrawipf]

Huge release with many fixes and new features. Dev version number is 1.9.x until now but it might as well be 2.0 for the release.

Matching configurator PR: https://github.com/Ultrawipf/OpenFFBoard-configurator/pull/50

Major changes for analog inputs:

• ADS1115 i²c ADC support
• common processing functions
• Analog lowpass filter per channel
• Manual analog ranges for processing (apin and ads111x)

Other changes:

• Added user configurable axis encoder ratios for setups with reductions
• Main effect loop runs in higher priority thread than idle
• Added effect filter option
• Added effects monitoring
• Added some analog autorange margin
• Added min/max commands for apin
• Added analog processing functions to ADS111X
• Selecting a "none" encoder will remove the axis value. Allows analog inputs to be used as the primary axis.
• Added constant force rate command
• String command parser uses a fixed ringbuffer to prevent allocations in ISR.
• Highly improved uart command stability (default baud rate 115200)