Big referencing refactor

- RC+RefCell pattern used... everywhere
- Ast type implemented
- unit tests for func_call
- more changes, but this commit scope has grown significantly and I
cannot list them all

src/eval.rs

@@ -15,8 +15,9 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
-use std::boxed::Box;
-use crate::cell::{Cell};
+use std::rc::Rc;
+use std::cell::RefCell;
+use crate::segment::{Ast};
 use crate::func::FTable;
 use crate::vars::VTable;
 
@@ -25,10 +26,10 @@ use crate::vars::VTable;
  * representing the simplest possible form of the input
  */
 pub fn eval(
-    _ast: &Box<Cell>,
-    _vars: &Box<VTable>,
-    _funcs: &Box<FTable>,
+    _ast: Ast,
+    _vars: Rc<RefCell<VTable>>,
+    _funcs: Rc<RefCell<FTable>>,
     _sym_loose: bool
-) -> Result<Box<Cell>, String> {
+) -> Result<Ast, String> {
     Err("Unimplemented".to_string())
 }