Version v0.05j "All it takes to stop the war in Ukraine is a phone ca…

…ll."

- Added two documentation files in /docs.
- Merged iannez pull request "Better use variables/constants". Thank you, excellent work!
- Added iannez as Collaborator at top of file comments.
- Preliminary work on adding EEPROM emulation in Flash to save operating parameters.
- Added "tab delimited data output" mode and commands to switch back and forth between formats.
- Removed (hopefully) all remaining code related to MCP4725 12-bit DAC.
- Better comments and code formatting.

Version v0.05i "Stop the war in Ukraine"

- ST7789 TFT LCD SPI display support.
- BMP280 sensor on I2C bus support.
- AHT20 support.
- TM1637 4-digit LED clock display support.
- MCP4725 I2C 12-bit DAC support deprecated.
- Program refactoring, better comments, various small bugs fixed.

Version v0.05f

- Added missing Bluetooth OCXO warmup messages
- OCXO warmup now a separate function from calibration
- Added countdown for calibration
- Added selectable calibration countdowns (15s or 60s)

Version v0.05e

- Check PWM input value in SP command (must be between 1 and 65535)

Version v0.05d

- Manual merge of ST7735 SPI color LCD support by Badwater-Frank.
- Preliminary work to support similar ST7789 SPI color LCD.
- More conditional compilation for MCP4725 I2C 12-bit DAC support.
- Moved setup() and loop() to bottom of source code file.

Version v0.05c

- Adds a command to set a PWM value between 1 and 65535.

Version v0.05b

- Added 2kHz test signal generator on pin PB5.
- Fixed bug in adjustVctlPWM() function which generated two adjustments
  when the OCXO frequency would come close to 10,000,000.000.
  Thanks to Badwater-Frank on the EEVBlog for the bug squashing.

Merge branch 'main' of https://github.com/AndrewBCN/STM32-GPSDO into …

…main

Added document comparing 16-bit PWM software DAC with 12-bit I2C DAC …

…module

Version v0.04f

Implements tunnel mode command and operation.
OLED display is now a configuration option
Work started on calibration process, command is implemented,
ongoing work on calibration algorithm.
16-bit PWM DAC tested and approved will replace 12-bit I2C DAC as
default hardware to generate Vctl in future versions.
Improved comments and variables names.