Got rid of "namespace" word in compiler code.

grammar/src/expressions.grm

@@ -122,7 +122,7 @@ atomicExpression
   : loop
   : SimpleName
   : FieldName
-  : "namespace" // for the root namespace
+  : "package" // for the root package
   ;
 
 label

grammar/src/lexical.grm

@@ -83,7 +83,7 @@ bq. See [Nonlocal returns and jumps]
 */
 
 /* Keywords:
-namespace
+package
 as
 type
 class

grammar/src/types.grm

@@ -32,7 +32,7 @@ selfType
   ;
 
 userType
-  : ("namespace" ".")? simpleUserType{"."}
+  : ("package" ".")? simpleUserType{"."}
   ;
 
 simpleUserType