Merge with `hardhat-abi-exporter`

[ItsNickBarry]

I'm considering merging this plugin with hardhat-abi-exporter and renaming it to hardhat-artifact-exporter or hardhat-exporter.

The plugins are almost exactly the same. These config options differ:

  spacing: number;
  pretty: boolean;
  filter: (
    abiElement: any,
    index: number,
    abi: any,
    sourceName: string,
    contractName: string,
  ) => boolean;
  format: 'minimal' | 'full' | 'json' | 'typescript';

[ItsNickBarry]

Include #9.