QuestDB configuration string parser

This is for:

• The questdb-confstr crate
• and its bindings for C questdb-confstr-ffi

Dev notes

To build and test:

cargo clean
cargo build
cargo test
cd questdb-confstr-ffi/cpp_test
./compile
./run

In addition, before pushing a PR, please run:

cargo fmt --all
cargo clippy --all-targets -- -D warnings