mark core as nostd

* implement custom hashmap to back symtable
* pass in print and read callbacks to keep stdlib pure
* use core / alloc versions of Box, Rc, Vec, etc
* replace pow func with libm

Signed-off-by: Ava Affine <ava@sunnypup.io>

core/src/lib.rs

@@ -15,7 +15,7 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
-//#![no_std]
+#![cfg_attr(not(test), no_std)]
 
 mod eval;
 mod lex;
@@ -24,6 +24,9 @@ mod stl;
 mod sym;
 mod error;
 
+#[macro_use]
+extern crate alloc;
+
 pub mod ast {
     pub use crate::eval::eval;
     pub use crate::lex::lex;