docs: Improve autogenerate godoc

There were a bunch of packages that weren't well documented. With the
recent split up of the lang package, I figured it would be more helpful
for new contributors who want to learn the structure of the project.

lang/types/doc.go

@@ -15,5 +15,5 @@
 // You should have received a copy of the GNU General Public License
 // along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
-// Package types provides a framework for our language values and types.
+// Package types provides a framework for our mcl language values and types.
 package types