Capture expression string from expectations

This allows a string that the user had in source code instead of a resolved value.

This change requires storing a 'label' and changing expectation and matcher constructor methods to macros.

src/spectator/dsl/example_dsl.cr

@@ -9,8 +9,8 @@ module Spectator
         expect(subject)
       end
 
-      def expect(actual : T) forall T
-        ::Spectator::Expectation.new(actual)
+      macro expect(actual)
+        ::Spectator::Expectation.new({{actual.stringify}}, {{actual}})
       end
     end
   end

src/spectator/dsl/matcher_dsl.cr

@@ -3,8 +3,8 @@ require "../matchers"
 module Spectator
   module DSL
     module MatcherDSL
-      def eq(expected : T) forall T
-        ::Spectator::Matchers::EqualityMatcher(T).new(expected)
+      macro eq(expected)
+        ::Spectator::Matchers::EqualityMatcher.new({{expected.stringify}}, {{expected}})
       end
     end
   end

src/spectator/expectation.cr

@@ -2,9 +2,10 @@ require "./matchers/matcher"
 
 module Spectator
   class Expectation(T)
+    private getter label : String
     getter actual : T
 
-    protected def initialize(@actual : T)
+    protected def initialize(@label : String, @actual : T)
     end
 
     def to(matcher : Matchers::Matcher)

src/spectator/matchers/equality_matcher.cr

@@ -3,7 +3,8 @@ require "./matcher"
 module Spectator
   module Matchers
     class EqualityMatcher(T) < Matcher
-      def initialize(@expected : T)
+      def initialize(label, @expected : T)
+        super(label)
       end
 
       def match?(expectation : Expectation)

src/spectator/matchers/matcher.cr

@@ -1,6 +1,11 @@
 module Spectator
   module Matchers
     abstract class Matcher
+      private getter label : String
+
+      private def initialize(@label : String)
+      end
+
       abstract def match?(expectation : Expectation)
     end
   end