feat(ast): add species base to template declarations

Added optional species_base field to Template struct enabling
template-species inheritance syntax: `template Name: Species { ... }`.
Updated LALRPOP grammar and all Template construction sites.

src/resolve/merge.rs

@@ -574,6 +574,7 @@ mod tests {
     ) -> Template {
         Template {
             name: name.to_string(),
+            species_base: None,
             fields,
             includes: includes.iter().map(|s| s.to_string()).collect(),
             strict,