Start adding eval and machine implementations, remove Inst for now

We're not compiling yet and mostly want to get the name stuff figured
out. Also may switch to using anyhow error handling.

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

src/vm/mod.rs

@@ -1,4 +1,3 @@
 pub mod error;
 pub mod eval;
-pub mod inst;
 pub mod machine;