feat: scaffold crate structure and implement core macros

Add the project skeleton, LICENSE files, README, Makefile, doc
examples, and the initial implementation of `#[func]`, `invoke!`,
and `select!` procedural macros.

1 files changed, 12 insertions, 0 deletions

diff --git a/doc/func.md b/doc/func.md
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+Attribute macro that generates both a sync and an async version of a function,
+gated by a Cargo feature flag.
+
+The function is written as a regular (non-async) `fn`. The macro duplicates it
+internally into two implementations:
+
+- When the feature is **disabled**: the original `fn` is used as-is.
+- When the feature is **enabled**: the function is promoted to `async fn`.
+
+By default the feature name is `"async"`. A different name can be supplied as
+an attribute argument, for example `#[func("tokio_rt")]` to gate on the feature
+`"tokio_rt"` instead.