Add configuration for MavenCentral publishing

[zsmb13]

Adds build configuration to publish the library to MavenCentral, based on this article and this library's config.

This will require the following inputs:

• signing.keyId: the ID of the GPG key pair used for signing, the last eight characters of its fingerprint
• signing.password: the passphrase of the key pair
• signing.secretKeyRingFile: the location of the exported private key
• ossrhUsername and osshrPassword: login credentials for https://oss.sonatype.org/
• stagingProfileId: value from Sonatype

Usage:

• Set the values described above in local.properties or environment variables
• ./gradlew assembleRelease (build)
• ./gradlew publishReleasePublicationToSonatypeRepository (sign and upload artifact to Sonatype)
• ./gradlew closeAndReleaseRepository (close and release Sonatype repo)

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I didn't include CI config in the first draft, but it would be fairly easy and convenient to plug this all into GitHub Actions.

[ursusursus]

bump please