Move matchers DSL into their own module

Moves the #eq method out of the global namespace.

src/spectator/dsl/example_dsl.cr

@@ -1,6 +1,10 @@
+require "./matcher_dsl"
+
 module Spectator
   module DSL
     module ExampleDSL
+      include MatcherDSL
+
       macro is_expected
         expect(subject)
       end

src/spectator/dsl/matcher_dsl.cr

@@ -0,0 +1,11 @@
+require "../matchers"
+
+module Spectator
+  module DSL
+    module MatcherDSL
+      def eq(expected : T) forall T
+        ::Spectator::Matchers::EqualityMatcher(T).new(expected)
+      end
+    end
+  end
+end

src/spectator/matchers/equality_matcher.cr

@@ -1,9 +1,5 @@
 require "./matcher"
 
-def eq(expected : T) forall T
-  Spectator::Matchers::EqualityMatcher(T).new(expected)
-end
-
 module Spectator
   module Matchers
     class EqualityMatcher(T) < Matcher