Update license to zlib.

And gitignore docs while we're at it.

.gitattributes

@@ -0,0 +1,2 @@
+
+doc/ linguist-vendored

LICENSE

@@ -0,0 +1,17 @@
+Copyright (c) 2019 Nicolas Hafner
+
+This software is provided 'as-is', without any express or implied
+warranty. In no event will the authors be held liable for any damages
+arising from the use of this software.
+
+Permission is granted to anyone to use this software for any purpose,
+including commercial applications, and to alter it and redistribute it
+freely, subject to the following restrictions:
+
+1. The origin of this software must not be misrepresented; you must not
+   claim that you wrote the original software. If you use this software
+   in a product, an acknowledgment in the product documentation would be
+   appreciated but is not required.
+2. Altered source versions must be plainly marked as such, and must not be
+   misrepresented as being the original software.
+3. This notice may not be removed or altered from any source distribution.

courier.asd

@@ -10,7 +10,7 @@
   :author "Nicolas Hafner <shinmera@tymoon.eu>"
   :maintainer "Nicolas Hafner <shinmera@tymoon.eu>"
   :version "1.2.0"
-  :license "Artistic"
+  :license "zlib"
   :description "An email marketing service for Radiance"
   :homepage "https://shirakumo.github.io/courier/"
   :bug-tracker "https://github.com/shirakumo/courier/issues"