v2.0 - State reporting, reliability, OTA, so much

Huge release, made possible with loads of testing by @austrisv and myself across two different continents and coordinated on the discord channel. Big changes are:

1. 📡 OTA Updating! There's now two methods:
   • via the [ip]/update page (or via curl command)
   • via loading from a http web server, initiated by the update= command. Can be sent, as always, via serial or http, and now via MQTT (see below!)
2. 🎙 Ability to send commands via the MQTT /cmd topic. For example on linux/mac: mosquitto_pub -L 'mqtt://myuser:mypassword@localhost/solar/mppt/cmd' -m version
3. 🌲 new log() function instead of printf. Sends to serial and to MQTT db. Allows you to see state changes, errors, etc, remotely.
4. 🌎 Now state-driven, can look at the state to see if the battery is:
   • in mppt mode, limited because the battery is full full_cv, current limited by configuration capped, off, sweeping, running in collapsemode (see below), or having issues with error state.
5. 🥣 Serial buffering for the CLI interface. Now it'll let you type-in input when using miniterm/screen/etc.
6. 🌥 New collapse-mode that will allow passthrough power from your panel to battery when that's the best option for the most power. Very useful on foggy/cloudy days, early/late in the day, or when there are lots of shadows on your panel.
7. New currFilt variable that shows a slowly filtered current value, this is used to restore from collapses much faster (and sent to mqtt for pretty charts)
8. 🔒 Added in mutex locking for shared resources so random reboots aren't a thing anymore. Days of uptime.
   • Added an uptime command. 😎
9. New backoff functionality that stops polling the DROK so frequently at night and when it's disconnected.
10. 🧹 Sweep now far more robust, detects full batteries, current caps, collapse-mode, and won't auto-run when not needed.