Solve #10, #11, add some additional features

[Ethosa]

• Fix toObject for runtime values (https://github.com/openpeeps/denim/pull/12/files#diff-86d904107e74d06b80c6f7718203ca025fec0ece6d8f39e2eeefa53877562214R226)
• Add hasOwnProperty procedure (https://github.com/openpeeps/denim/pull/12/files#diff-86d904107e74d06b80c6f7718203ca025fec0ece6d8f39e2eeefa53877562214R316-R321)
• fix callFunction proc (#10) (https://github.com/openpeeps/denim/pull/12/files#diff-86d904107e74d06b80c6f7718203ca025fec0ece6d8f39e2eeefa53877562214R450)
• improve callMethod proc (https://github.com/openpeeps/denim/pull/12/files#diff-86d904107e74d06b80c6f7718203ca025fec0ece6d8f39e2eeefa53877562214R455)
• export_napi now works with Nim 2.0.0 (#11) (https://github.com/openpeeps/denim/pull/12/files#diff-86d904107e74d06b80c6f7718203ca025fec0ece6d8f39e2eeefa53877562214R581-R601)
• add some methods to work with napi_coerce_to... (https://github.com/openpeeps/denim/pull/12/files#diff-86d904107e74d06b80c6f7718203ca025fec0ece6d8f39e2eeefa53877562214R722-R732)
• napi_get_property_names (https://github.com/openpeeps/denim/pull/12/files#diff-86d904107e74d06b80c6f7718203ca025fec0ece6d8f39e2eeefa53877562214R735-R747)
• pairs iterator for napi_object (https://github.com/openpeeps/denim/pull/12/files#diff-86d904107e74d06b80c6f7718203ca025fec0ece6d8f39e2eeefa53877562214R758-R762)
• convenient $ nim proc (https://github.com/openpeeps/denim/pull/12/files#diff-86d904107e74d06b80c6f7718203ca025fec0ece6d8f39e2eeefa53877562214R770-R786)

[horanchikk]

DENIM DEVELOPER AT THIS MOMENT

[georgelemon]

This is great! Thanks