Add a lot of new stuff to the compile mod

* compile::sym is now compile::name
* add basic block structure
* add visitor pattern
* some other minor things (e.g. syn::ast::prelude)

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

src/compile/visit.rs

@@ -0,0 +1,29 @@
+use crate::syn::ast::{Stmt, Expr};
+
+pub trait Visit {
+    type Out;
+    fn visit<A: Accept<Self>>(&mut self, acceptor: &A) -> Self::Out
+        where Self: Sized
+    {
+        acceptor.accept(self)
+    }
+
+    fn visit_stmt(&mut self, stmt: &Stmt) -> Self::Out;
+    fn visit_expr(&mut self, expr: &Expr) -> Self::Out;
+}
+
+pub trait Accept<V: Visit> {
+    fn accept(&self, visitor: &mut V) -> V::Out;
+}
+
+impl<V: Visit> Accept<V> for Stmt {
+    fn accept(&self, visitor: &mut V) -> V::Out {
+        visitor.visit_stmt(self)
+    }
+}
+
+impl<V: Visit> Accept<V> for Expr {
+    fn accept(&self, visitor: &mut V) -> V::Out {
+        visitor.visit_expr(self)
+    }
+}