Coding rules and specs update

Author: tomaka

README.md

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+# Coding rules
+
+- No global variables. No thread-local variables. No global logger or anything similar.
+- No sleeping a thread. Everything asynchronous.
+- Panic as soon as something weird is detected. Don't try to continue running the program if we detect a state inconsistency.
+- Code sharing between components kept to a minimum. Code must be isolated as much as possible.
+- Things like Prometheus or RPC endpoints must not be rooted deep in the code. It must theoretically be easy to remove support for Prometheus or the RPC server from this library. Prefer pulling information from components from a higher-level rather than passing `Arc` objects around.
+- Rustfmt is used.