XS_PLUGIN and XS_FILTER implementation

This patch introduces following features:
- XS_PLUGIN context option to add plugins to libxs
- XS_FILTER option to switch between different filter types
- Automatic loading of plug-ins is *not* implemented.

From the implementation point of view:
- standard prefix filter is implemented as a pluggable filter
- trie_t and mtrie_t are joined into a single class
- the code for 0MQ/3.1 compatibility is left in in the form of comments
- new test for testing re-subscriptions is added
Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/.gitignore b/.gitignore
index 2b25d2a..ce92051 100644
--- a/.gitignore
+++ b/.gitignore
@@ -40,6 +40,8 @@ tests/max_sockets
 tests/emptyctx
 tests/polltimeo
 tests/wireformat
+tests/libzmq21
+tests/resubscribe
 src/platform.hpp*
 src/stamp-h1
 perf/local_lat