Add debugging interface.

Cargo.toml

@@ -44,6 +44,7 @@ no_module = []                  # no modules
 internals = []                  # expose internal data structures
 unicode-xid-ident = ["unicode-xid"] # allow Unicode Standard Annex #31 for identifiers.
 metadata = ["serde", "serde_json", "rhai_codegen/metadata", "smartstring/serde"] # enable exporting functions metadata
+debugging = ["internals"]       # enable debugging
 
 no_std = ["no-std-compat", "num-traits/libm", "core-error", "libm", "ahash/compile-time-rng"]
 
@@ -101,4 +102,4 @@ optional = true
 instant = { version = "0.1.10" } # WASM implementation of std::time::Instant
 
 [package.metadata.docs.rs]
-features = ["metadata", "serde", "internals", "decimal"] # compiling for no-std
+features = ["metadata", "serde", "internals", "decimal", "debugging"]