Support for other EVM based Etherscan chains

[miohtama]

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The README mentions Ropsten, Kovan, etc.

But is the library compatible with other L1 or L2 based chains that run their own hosted EtherScan instances, like polygonscan.com?

[github-actions[bot]]

Thanks for reporting this issue, we are on it :)

[gnarvaja]

I submitted this #27 that adds support for Polygon and allows to easily support other instances when the domain is not etherscan.io.