bATtiny Guard - Power Management module

A small update to the firmware has been made to make it work properly with revised hardware. A driver MOSFET has been added to improve performance and to invert driving logic of the output MOSFET so it turns on when the uC pin is driven high. This revision also eliminates problems with unpredictable behavior upon connecting the battery and/or module entering UVLO which would cause the output MOSFET to unexpectedly to turn on.

A PDF with all 6 layers of the module PCB has been added to the documentation for easier viewing without unpacking gerber or source files.

Next step is to implement an additional I2C port in firmware to allow the module to act as a master to on-board devices (which it does currently through the hardware I2C) and as a slave to external master. I expect to have this implemented and tested in the next few weeks.

I have been testing the new 0.8mm PCB for about two weeks under load now, and it appears to perform as expected and with excellent stability without issues for the whole duration of testing.
Testing will continue, even tho it probably is proven to work reliably for long periods of time at this point.

The default firmware for the module got an update. Now it works based on interrupts, so the cpu is in standby mode most of the time which has major power saving benefits. It wakes up once a second to do the readings and send them over serial, this works by using RTC overflow interrupt. Also it's waken up by pressing the buttons which starts a timer which tracks how long the buttons have been pressed to realize a smooth on/off operation.

Future firmware upgrades include a full separate i2c interface so Attiny can be accessed easily externally while also being a master for on-board devices.

Aside from firmware, EAGLE and KiCad footprints have been added.