mce-proc - Markdown Code Extractor procedural macros

See and use Markdown Code Extractor prudent/mce.

Other details

Configuration in TOML only

See prudent/mce -> README.md for why configuration is in TOML only.

nth*** and mce_tag*** extractions do repeat parsing

Every invocation of nth*** and mce_tag*** extraction macros do parse the whole file (README.md or as configured). The cost is irrelevant, and for must use cases negligible. We do NOT cache/store any data/content between the macro invocations. Why? Rust macros must not keep/depend on any state between their invocations.