Yaroslav Skopets

## Summary * add API to mutate data in `Envoy` buffer, i.e. data of TCP connection and HTTP request/response body

## Context * Follow up for #39

## Context * `Rust` doesn't support backtraces on `wasm32` (neither is [backtrace](https://docs.rs/backtrace/0.3.50/backtrace/) package) ## Expected * find a way for user to manually attach location to an error * use...

## Context * native `Envoy` `Network Filters` can stop further processing of a TCP connection by using `read_callbacks_->connection().close(...)` API ## Expect * `proxy-wasm` spec should provide an equivalent ABI