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/lib.rs

@@ -15,18 +15,18 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
-mod cell;
+mod segment;
 mod lex;
 mod func;
 mod eval;
 mod vars;
 
 pub mod ast {
-    pub use crate::cell::{Cell, Ctr, cons, cell_as_string};
+    pub use crate::segment::{Seg, Ctr, ast_to_string, Type, Ast, new_ast};
     pub use crate::lex::lex;
     pub use crate::func::{Function, Operation, FTable, Args,
                           InternalOperation, ExternalOperation,
-                          declare};
-    pub use crate::vars::VTable;
+                          func_declare, func_call};
+    pub use crate::vars::{VTable, define};
     pub use crate::eval::eval;
 }