[FIX] Critical fix - spawn should inherit onmiss functionality (#40)

Add "has" method for checking if keys exist

Add onempty handler

Support a list of keys

Fix priority of scope lookup: results should prefer to scoped (#32)

Scoped results should prefer to scoped result when a scope is supplied

Memoise - improve instance subsequent key lookups

Expose instance - made for Webpack externa

Lock singleton to global, add onmiss entry point

Introduce a child process - namespaced instance

Add singleton to interface