Improve error locations

tests/BadImport.newt

@@ -0,0 +1,4 @@
+module BadImport
+
+-- Error should point to name here
+import Does.Not.Exist

tests/BadImport.newt.fail

@@ -0,0 +1,2 @@
+*** Process tests/BadImport.newt
+ERROR at tests/BadImport.newt:4:8--4:22: error reading tests/Does/Not/Exist.newt: Error: ENOENT: no such file or directory, open 'tests/Does/Not/Exist.newt'

tests/ErrorDup.newt

@@ -0,0 +1,9 @@
+module ErrorDup
+
+data Nat = Z | S Nat
+
+data Nat = Z | S Nat
+
+record Nat where
+
+class Nat where

tests/ErrorDup.newt.fail

@@ -0,0 +1,21 @@
+*** Process tests/ErrorDup.newt
+module ErrorDup
+ERROR at tests/ErrorDup.newt:5:6--5:9: Nat already declared
+  data Nat = Z | S Nat
+  
+  data Nat = Z | S Nat
+       ^^^
+
+ERROR at tests/ErrorDup.newt:7:8--7:11: Nat already declared
+  data Nat = Z | S Nat
+  
+  record Nat where
+         ^^^
+
+ERROR at tests/ErrorDup.newt:9:7--9:10: Nat already declared
+  record Nat where
+  
+  class Nat where
+        ^^^
+
+Compile failed