Implement return hooks for Lua functions (zero-cost if disabled).

doc/changes.html

@@ -56,7 +56,7 @@ to see whether newer versions are available.
 <h2 id="snap">Development Snapshot</h2>
 <ul>
 <li>Build of preliminary x64 interpreter works on Linux/x64 or WIN64.</li>
-<li>Implement call hooks (zero-cost if disabled).</li>
+<li>Implement call/return hooks (zero-cost if disabled).</li>
 <li>Major redesign of internal function call handling.</li>
 <li>Implement yield from C hooks.</li>
 <li>Add abstract C call handling to IR.</li>