LNPBP-2 rewrite & finalization

[dr-orlovsky]

• Description of a commitment procedure for a set of pubkeys from script was moved to LNPBP-1 and merged with the commitment procedure there: https://github.com/LNP-BP/LNPBPs/issues/48 & https://github.com/LNP-BP/LNPBPs/pull/67
• Updated miniscript version
• Updated rationale
• Changed OP_RETURN commitment details
• Closed issues from #41
• Modernized references
• Fixed issue with absence of redeemScript/witnessScript distinguishing