Do not expose Trait and Module by default

This allows custom modules to define types with the name Trait or
Module. To use Trait and Module you just import them from std::trait and
std::module respectively. The module std::module does not define
anything useful at this time, but more useful code will be added to it
in the future.

runtime/src/core/globals.inko

@@ -12,5 +12,3 @@ let Integer = Inko::Integer
 let Float = Inko::Float
 let Block = Inko::Block
 let Array = Inko::Array
-let Trait = Inko::Trait
-let Module = Inko::Module

runtime/src/core/prelude.inko

@@ -35,6 +35,7 @@ import std::process
 import std::vm
 import std::range::(Range as _Range)
 import std::integer::extensions
+import std::module
 # These constants are re-exported so they're available to all modules by
 # default. Core types such as String should be exposed in std::globals instead.

runtime/src/std/mirror.inko

@@ -75,7 +75,8 @@
 # particular a mirror has to be allocated every time you need one. As such we
 # recommend against using reflection in performance critical code.
 import std::fs::path::Path
-import std::trait::IMPLEMENTED_TRAITS_ATTRIBUTE
+import std::module::Module
+import std::trait::(IMPLEMENTED_TRAITS_ATTRIBUTE, Trait)
 # The default name to use for objects that don't have an explicit name.
 let DEFAULT_OBJECT_NAME = 'Object'

runtime/src/std/module.inko

+# Modules of Inko source code.
+
+# A collection of types and methods.
+#
+# A `Module` is an object created for every module of Inko source code, and
+# contains data such as the methods defined in the module.
+#
+# Modules are permanent objects, and are never garbage collected.
+let Module = Inko::Module

runtime/src/std/trait.inko

 # Methods for `Trait` that should be available before defining other types.
+# The object traits are instances of.
+let Trait = Inko::Trait
+
 # The name of the attribute that stores all the implemented traits.
 let IMPLEMENTED_TRAITS_ATTRIBUTE = '@_implemented_traits'