Make `muse-project-alist' more intuitively customizable.

Make `muse-project-alist' more intuitively customizable.

* examples/mwolson/muse-init.el (muse-project-alist): Resync with my
  settings.

* lisp/muse-project.el: Thanks to jessealama on IRC for the suggestion.
  (muse-project-alist-get): New function that pre-parses
  `muse-projects-alist' before customization in order to work around an
  annoying limitation in the customize interface.
  (muse-project-alist-set): New function that takes the value that
  customize gave us and turns it into something Muse can use.
  (muse-project): New widget that outlines the form of the
  `muse-project-alist' variable.
  (muse-project-alist): Use the `muse-project' widget and specify :set
  and :get.
git-archimport-id: mwolson@gnu.org--2005/muse--main--1.0--patch-125