v6.4.0

• chore: merge master into 6.x (5c430cc)
• feat: add computeSignatureAsync() and checkSignatureAsync(), fix asynchronous verification through a callback, and deprecate the callback form (#657) (84df780)
• chore: deprecate signing and verifying a document that has a DOCTYPE (#661) (8a7e264)
• chore: warn about input that 7.0 rejects (#660) (b4f1335)
• chore: deprecate renderNs() and processInner() ahead of 7.0 (#656) (6004896)
• chore: deprecate enveloped-signature after a canonicalization (#649) (557dfff)
• feat: check private-key data against its label in toPem() and pemToDer() (#658) (0c38c80)
• chore: put the lockfile back in sync for npm 8 (#659) (f844ded)
• chore: group tests and deprecations in the changelog (#651) (a311adc)