api: add Dialer interface and implementation

The patch adds ability to mock network connection to a Tarantool
instance.

The default implementation can be used as a basic building block
for another package or a connector.

Part of tarantool/roadmap-internal#197

Author: oleg-jukovec

CHANGELOG.md

@@ -12,6 +12,8 @@ Versioning](http://semver.org/spec/v2.0.0.html) except to the first release.
 
 - Support pagination (#246)
 - A Makefile target to test with race detector (#218)
+- An ability to replace a base network connection to a Tarantool
+  instance (#265)
 
 ### Changed