Add match data docs

src/spectator/matchers/failed_match_data.cr

@@ -1,15 +1,20 @@
 require "./match_data"
 
 module Spectator::Matchers
+  # Information about a failed match.
   struct FailedMatchData < MatchData
+    # Indicates that the match failed.
     def matched?
       false
     end
 
+    # Description from the matcher as to why it failed.
     getter failure_message : String
 
+    # Additional information from the match that can be used to debug the problem.
     getter values : Array(Tuple(Symbol, String))
 
+    # Creates the match data.
     def initialize(@failure_message, **values)
       @values = values.to_a
     end

src/spectator/matchers/match_data.cr

@@ -1,5 +1,7 @@
 module Spectator::Matchers
+  # Information about the outcome of a match.
   abstract struct MatchData
+    # Indicates whether the match as successful or not.
     abstract def matched? : Bool
   end
 end

src/spectator/matchers/successful_match_data.cr

@@ -1,7 +1,9 @@
 require "./match_data"
 
 module Spectator::Matchers
+  # Information about a successful match.
   struct SuccessfulMatchData < MatchData
+    # Indicates that the match succeeded.
     def matched?
       true
     end