add zsh completion support

```diff
diff --git a/PKGBUILD_20131221_180654 b/PKGBUILD
index 24e4f8e..4bd84f8 100644
--- a/PKGBUILD_20131221_180654
+++ b/PKGBUILD
@@ -22,8 +22,9 @@ pkgver() {
 
 package() {
     cd "$srcdir/$_pkgname"
-    mkdir -p "$pkgdir"/{usr/bin,etc/bash_completion.d,usr/share/man/man8}
+    mkdir -p "$pkgdir"/{usr/bin,etc/bash_completion.d,/usr/share/zsh/site-functions,usr/share/man/man8}
     cp owlman owlman_* "$pkgdir/usr/bin"
     cp bash_completion.d/* "$pkgdir/etc/bash_completion.d"
+    cp zsh_completion/* "$pkgdir/usr/share/zsh/site-functions"
     cp owlman.8 "$pkgdir/usr/share/man/man8"
 }
```