v2.0.0 - package rewrite

✨ re-write package

Now exports 2 functions:

• makeExecutableSchema which is essentially what this package was before
• combineSchemaDefinitions which combines the schemas but doesn't convert to a GraphQL AST yet

This helps be more compatible with different GraphQL servers.

Also, the package now handles comining schemaDirectives.

This uses merge from unchanged which should be a tiny bit smaller and faster than the same method from lodash.merge.