Draft for p2sh multisig wallet structure

Discussion: https://www.mail-archive.com/bitcoin-development@lists.sourceforge.net/msg05156.html
Please don't add a project-wide gitignore. Gitignore is meant for temporary files that are generated during the build process. We don't have a build system for bips, so there are none.
There are various other ways in which you can see local ignore rules, see https://help.github.com/articles/ignoring-files/