New node specification. This totally breaks compatibility.

So, before the BMS is in production (and it's currently testing in
only one system), I want to break the compatibility NOW if ever.
The new spec makes some if statements simpler, removes unnecessary,
adds new features + leaves more reserved bits for future modifications
without breaking compatibility.
Bmsnode rewrite to new spec

- Command/reply codes changed
- Long measurement mode (to prevent aliasing)
- Brown-out detector disable mode (to reduce quiescent current even further)
- Version number reporting
- etc.