Improve documentation; Split tests into separate file
Fix cloning of deeply-wrapped funs
Allow cloning of combined futures
Rewrite most code to properly monitor futures which we interact with
Return error(badfuture) if someone tries to bound already bounded future
Properly handle future and future's worker processes terminations
Implement collect_any/1 to select any successful future
Reorganize combine/2 and select/2 compositions;
Export low-level API for writing custom wrappers;
Add wait_for/1, on_done/2, on_success/2 and on_failure/2;
Throw exceptions when trying to set/2 or execute/2 for wrapping futures
Update README