Document Scheduler, ThreadPoolScheduler and CurrentThreadScheduler

WANTED

@@ -16,7 +16,6 @@ Tutorials:
 
 API docs:
     * MOP
-    * Scheduler
     * KeyReducer
 
 Builtins:

lib/Type/CurrentThreadScheduler.pod

@@ -0,0 +1,12 @@
+=begin pod
+
+=TITLE class CurrentThreadScheduler
+
+=SUBTITLE A simple scheduler that blockingly executes code on the current thread
+
+    class CurrentThreadScheduler does Scheduler { ... }
+
+C<CurrentThreadScheduler> executes tasks on the current threads. This means
+that L<#method cue> blocks until the code has finished executing.
+
+=end pod

lib/Type/Scheduler.pod

@@ -0,0 +1,47 @@
+=begin pod
+
+=TITLE role Scheduler
+
+=SUBTITLE Common roles for (thread/task) schedulers
+
+    role Scheduler {
+        has &.uncaught_handler is rw
+    }
+
+Common role for schedulers. A scheduler is a piece of code that determines
+which resources to use to run which task, and when.
+
+Some operations for example on L<Proc::Async>, L<Promise|/type/Promise>,
+L<Supply|/type/Supply> allow you to specify a scheduler explicitly; they
+generally expect those schedulers to follow the interface defined by
+C<Scheduler>
+
+=head1 Methods
+
+=head2 method uncaught_handler
+
+    method uncaught_handler() is rew
+
+RW-Accessor for the handler that is caught for uncaught exceptions from the
+code that is being scheduled and run.
+
+=head2 method cue
+
+    method cue(:&code, Instant :$at, :$in, :$every, :$times = 1; :&catch)
+
+Schedules a callable (C<&code>) for execution. The adverbs control when how
+and the code is run:
+
+C<$at> can be an L<Instant|/type/Instant> before which the code won't be run.
+Alternatively C<$in> is the number of seconds (possibly fractional) to wait
+before running the code.
+
+If C<$every> is specified, it is interpreted as the number of seconds
+(possibly fractional) to wait before re-executing the code.
+
+C<$times> tells the scheduler how many times to run the code.
+
+C<&catch> is called with the L<Exception|/type/Exception> as its sole argument
+if C<&code> dies.
+
+=end pod

lib/Type/ThreadPoolScheduler.pod

@@ -0,0 +1,23 @@
+=begin pod
+
+=TITLE class ThreadPoolScheduler
+
+=SUBTITLE Scheduler that distributes work among a pool of threads
+
+    class ThreadPoolScheduler does Scheduler { ... }
+
+The C<ThreadPoolScheduler> has a range of number of threads that it maintains,
+and it distributes work among those threads. When the upper limit of threads
+isn't reached yet, and there is work pending, it spawns new threads to handle
+the work.
+
+=head1 Methods
+
+=head2 new
+
+    method new(Int :$initial_threads = 0, Int :$max_threads=16)
+
+Creates a new C<ThreadPoolScheduler> object with the given range of threads to
+maintain.
+
+=end pod