Most files suffered major changes

- Less ambiguous syntax
- Better parser (Chumsky only does tokenization now)
- Tidy(|ier) error handling
- Facade for simplified embedding
- External code grouped in (fairly) self-contained Systems
- Dynamic action dispatch
- Many STL additions

src/foreign/mod.rs

@@ -0,0 +1,17 @@
+//! Interaction with foreign code
+//!
+//! Structures and traits used in the exposure of external functions and values
+//! to Orchid code
+mod atom;
+pub mod cps_box;
+mod extern_fn;
+
+use std::rc::Rc;
+
+pub use atom::{Atom, Atomic, AtomicResult, AtomicReturn};
+pub use extern_fn::{ExternError, ExternFn, XfnResult};
+
+pub use crate::representations::interpreted::Clause;
+
+/// A type-erased error in external code
+pub type RcError = Rc<dyn ExternError>;