Use standard log utility

src/spectator/example.cr

@@ -28,7 +28,7 @@ module Spectator
     # Returns the result of the execution.
     # The result will also be stored in `#result`.
     def run : Result
-      Spectator.debug("Running example #{self}")
+      Log.debug { "Running example #{self}" }
       @delegate.call(self)
       raise NotImplementedError.new("#run")
     end

src/spectator/spec_builder.cr

@@ -8,6 +8,8 @@ module Spectator
   # A stack is used to track the current example group.
   # Adding an example or group will nest it under the group at the top of the stack.
   class SpecBuilder
+    Log = ::Spectator::Log.for(self)
+
     # Stack tracking the current group.
     # The bottom of the stack (first element) is the root group.
     # The root group should never be removed.
@@ -36,7 +38,7 @@ module Spectator
     # The newly created group is returned.
     # It shouldn't be used outside of this class until a matching `#end_group` is called.
     def start_group(name, source = nil) : ExampleGroup
-      Spectator.debug("Start group: #{name.inspect} @ #{source}")
+      Log.trace { "Start group: #{name.inspect} @ #{source}" }
       ExampleGroup.new(name, source, current_group).tap do |group|
         @group_stack << group
       end
@@ -49,7 +51,7 @@ module Spectator
     # At this point, it is safe to use the group.
     # All of its examples and sub-groups have been populated.
     def end_group : ExampleGroup
-      Spectator.debug("End group: #{current_group}")
+      Log.trace { "End group: #{current_group}" }
       raise "Can't pop root group" if root?
 
       @group_stack.pop
@@ -74,7 +76,7 @@ module Spectator
     #
     # The newly created example is returned.
     def add_example(name, source, context, &block : Example, Context ->) : Example
-      Spectator.debug("Add example: #{name} @ #{source}")
+      Log.trace { "Add example: #{name} @ #{source}" }
       delegate = ExampleContextDelegate.new(context, block)
       Example.new(delegate, name, source, current_group)
       # The example is added to the current group by `Example` initializer.