Add curve functions wrappers (#671)

* Add curve functions wrappers

* Add curve CI job and fix the libzmq build

tests/curve.cpp

@@ -0,0 +1,36 @@
+#include <catch2/catch_all.hpp>
+#include <zmq.hpp>
+
+#ifdef ZMQ_HAVE_CURVE
+
+TEST_CASE("curve_keypair", "[curve]")
+{
+    auto keys = zmq::curve_keypair();
+    auto public_key = keys.first;
+    auto secret_key = keys.second;
+    CHECK(!public_key.empty());
+    CHECK(!secret_key.empty());
+}
+
+TEST_CASE("curve_public", "[curve]")
+{
+    auto secret_key = "D:)Q[IlAW!ahhC2ac:9*A}h:p?([4%wOTJ%JR%cs";
+    auto public_key = zmq::curve_public(secret_key);
+    CHECK(public_key == "Yne@$w-vo<fVvi]a<NY6T1ed:M$fCG*[IaLV{hID");
+}
+
+#endif
+
+TEST_CASE("z85_encode", "[curve]")
+{
+    std::vector<uint8_t> data{1,2,3,4,5,6,7,8};
+    auto encoded = zmq::z85_encode(data);
+    CHECK(encoded.size() == std::string("0rJua1Qkhq").size());
+    CHECK(encoded == "0rJua1Qkhq");
+}
+
+TEST_CASE("z85_decode", "[curve]")
+{
+    auto decoded = zmq::z85_decode("0rJua1Qkhq");
+    CHECK(decoded == std::vector<uint8_t>{1,2,3,4,5,6,7,8});
+}