Split Engine into eval folder.

src/eval/mod.rs

@@ -0,0 +1,15 @@
+mod chaining;
+mod data_check;
+mod eval_context;
+mod eval_state;
+mod expr;
+mod global_state;
+mod stmt;
+mod target;
+
+#[cfg(any(not(feature = "no_index"), not(feature = "no_object")))]
+pub use chaining::{ChainArgument, ChainType};
+pub use eval_context::EvalContext;
+pub use eval_state::EvalState;
+pub use global_state::GlobalRuntimeState;
+pub use target::Target;