Prepare 0.3.1 release

0.3.0 release for 2.13 compat

Fix the fix for oleg-py#12 - used & instead of |

Fix oleg-py#12: mark synthetic params as such when untupling

Require a type decl for implicit patterns

Change version; make wrong patterns error instead of crashing scalac

Fix: unable to do destructuring in for bindings

Fix: _ = println("...") caused unused warning

Add Either test. Preparation for 0.2.0 release

Add README