Creates a new file for statement prefixes.

This is for #534, but mainly for #2034
Still way to go.

doc/Language/00-POD6-CONTROL

@@ -80,6 +80,7 @@ Quoting constructs FILE: quoting
 Regexes FILE: regexes
 Routines FILE: routines
 Sets, bags, and mixes FILE: setbagmix
+Statement prefixes FILE: statement-prefixes
 Subscripts FILE: subscripts
 Syntax FILE: syntax
 System interaction FILE: system

doc/Language/statement-prefixes.pod6

@@ -0,0 +1,39 @@
+=begin pod :tag<perl6>
+
+=TITLE Statement prefixes
+
+=SUBTITLE Prefixes that alter the behavior of a statement of set of them
+
+Statement prefixes are not statements per se. They are written in front of a
+statement, and change their meaning, their output, or the moment they are going
+to be run. Since they have a specific behavior, they are also sometimes specific
+to some statement or statements.
+
+=head2 X<C<lazy>|lazy (statement prefix)>
+
+As a statement prefix, lazy acts on C<for> loops, saving the execution for when
+the variable they are assigned for is actually needed.
+
+=for code
+my $incremented = 0;
+my $var = lazy for <1 2 3 4> -> $d {
+    $incremented++
+};
+say $incremented; # OUTPUT: «0␤»
+say eager $var;   # OUTPUT: «(0 1 2 3)␤»
+say $incremented; # OUTPUT: «4␤»
+
+The C<$incremented> variable is only incremented, that is, the internal part of
+the loop is only run, when we eagerly evaluate the variable C<$var> that
+contains the lazy loop. Eagerness can be applied on a variable in other ways,
+such as calling the C<.eager> method on it.
+
+This prefix can also be used
+L<in front of C<gather>|/language/control#gather/take> to make the inner
+statements behave lazily.
+
+
+
+=end pod
+
+# vim: expandtab softtabstop=4 shiftwidth=4 ft=perl6