Fix some links

This is going to help with #561 a bit.

There are probably better ways to fix these links, but that's good enough.

Author: AlexDaniel

doc/Language/operators.pod

@@ -503,7 +503,7 @@ Technically this is not an operator, but syntax special-cased in the compiler.
 =head2 postfix C«.=»
 
 A X<mutating method call>. C<$invocant.=method> desugars to
-C<$invocant = $invocant.method>, similar to L<C<op=>>.
+C<$invocant = $invocant.method>, similar to L<C<=>>.
 
 Technically this is not an operator, but syntax special-cased in the compiler.
 

doc/Type/CurrentThreadScheduler.pod

@@ -7,6 +7,7 @@
     class CurrentThreadScheduler does Scheduler { ... }
 
 C<CurrentThreadScheduler> executes tasks on the current threads. This means
-that L<Scheduler#method cue> blocks until the code has finished executing.
+that L<method cue|/type/Scheduler#method cue> blocks until the code has
+finished executing.
 
 =end pod

doc/Type/Dateish.pod

@@ -63,7 +63,8 @@ L<Str|/type/Str>. If none was provided at object construction, a
 default formatter is used.  In that case the method will return a
 Callable type object.
 
-The formatting function is called by L<DateTime#method Str> with the
+The formatting function is called by
+L<DateTime method Str|/type/DateTime#method Str> with the
 invocant as its only argument.
 
     my $dt = Date.new('2015-12-31');  # (no formatter specified)

doc/Type/Mu.pod

@@ -156,8 +156,8 @@ Classes may provide their own C<new> method to override this default.
 
 C<new> triggers an object construction mechanism that calls submethods named
 C<BUILD> in each class of an inheritance hierarchy, if they exist. See
-L<the documentation on object construction|/language/objects#Object
-Construction> for more information.
+L<the documentation on object construction|/language/objects#Object Construction>
+for more information.
 
 =head2 method bless