Merge #16: init: elip for discounted CT

33e5c4d ELIP-0200: Discounted fees for Confidential Transactions (Byron Hambly)

Pull request description:

  first pass at ELIP for discounted CT as implemented in ElementsProject/elements#1317 and alternate implementation in ElementsProject/rust-elements#204

ACKs for top commit:
  apoelstra:
    utACK 33e5c4d -- did not verify the test vectors

Tree-SHA512: 1c2d10a7e6ae0750e53e2364f4a55a767fa99d600bf5a9eaa04f3b06d906e618c6b9f0097ab829c651a3152cf5e0475109de045b8c9109892cea81844893a000

elip-0150.mediawiki

@@ -5,7 +5,7 @@
   Author: Andrew Poelstra <apoelstra@blockstream.com>
           Tim Ruffing <crypto@timruffing.de>
   Comments-Summary: No comments yet.
-  Comments-URI: https://github.com/ElementsProject/elips/wiki/Comments:ELIP-????
+  Comments-URI: https://github.com/ElementsProject/elips/wiki/Comments:ELIP-0150
   Status: Draft
   Type: Standards Track
   Created: 2022-10-06
@@ -190,4 +190,3 @@ Finally, the following are invalid test vectors that should not be parseable:
 ==Acknowledgements==
 
 We would like to thank Leo Comandini for describing practical requirements by wallet authors, and to Jonas Nick for providing feedback on the cryptographic design.
-