Move classes under Spectator::Core

src/spectator.cr

@@ -1,3 +1,5 @@
+require "./spectator/core/**"
+
 # Feature-rich testing framework for Crystal inspired by RSpec.
 module Spectator
   # Current version of the Spectator library.

src/spectator/core/example.cr

@@ -1,4 +1,4 @@
-module Spectator
+module Spectator::Core
   # Information about a test case and functionality for running it.
   class Example
     # Name of the example.

src/spectator/core/example_group.cr

@@ -1,4 +1,4 @@
-module Spectator
+module Spectator::Core
   # Information about a group of examples and functionality for running them.
   # The group can be nested.
   class ExampleGroup