Bump version to 0.0.18

Overview of changes:

 *  Improved logic of CA certificate storage

    Now imapdomo will only default to local 'certificates' file if it
    exists -- if it does not exist it will leave -t option for
    imapfilter alone, meaning that the system storage will be used.

    Both behaviors can be forced on command line by -t or -T arguments.

 *  Added few missing option description in usage message

mkit.ini

@@ -1,5 +1,5 @@
 [project]
-    version     = 0.0.17
+    version     = 0.0.18
     name        = imapdomo
     pkgname     = imapdomo
     maintainer  = Alois Mahdal <netvor+imapdomo@vornet.cz>