add support for metadata

[k-yle]

hi, i see that this repository is active again, so I'd like to raise a PR for the changes that we made in our fork a few years ago. It would be nice to get this merged into the official package :)

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Here's the reason for this change 🚀

It's useful to have access to the metadata inside the pbf file. For example, when building QA tools for OSM.

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Here's what actually got changed 👏

This is based on #81, which is 5 years out of date. The main changes are:

• added all metadata fields, not just Timestamp and Version
• added test cases
• rebased onto master

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Here's how others can test the changes 👀

• end-to-end tests in this repository
• end-to-end tests in a tool that imports this library: osm-nz/linz-address-import@c64fc9b
• by manually editing package.json to point to this branch (example)

Superseeds / Closes #81