Implement REPL CLI command

[MaxDesiatov]

A simple typology command should launch a new REPL instance that's ready to parse given Swift code and build an environment from it.

repl command should allow invocations of the form typology repl File.swift that parses the file and starts a REPL with all declarations in that file already available in scope.

So far it looks like Linenoise library would be the best option to try at first for the REPL implementation.