Low level bindings to nodejs' N-API

Features

Different API versions may be selected via feature-flag. See the N-API Version Matrix for details.

• napi_v5 supported by all actively maintained NodeJS releases
• napi_v6 requires at least v13.7.0, this is the default (if no flag is given)
• the experimental N-API features may be enabled via feature flag experimental (off by default)