Build Repl.Lib when building Repl bundle

[alfonsogarciacaro]

To prevent compiler version mismatches as it happened in #80. This means that Repl.Lib build should be moved to the Fable repo (and maybe we should do the same with the .dll metadata which is duplicated right now). Maybe it's a good idea so we can also bundle the Repl.Lib with the pure-JS fable-compiler and allow people build simple apps with it.