Add preliminary license

License.txt

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+The core ideas used in this PHPSkills project were described in 
+"TrueSkill (TM): A Bayesian Skill Rating System" available at 
+http://research.microsoft.com/apps/pubs/default.aspx?id=67956
+
+The authors of the above paper have asked for a link to that article
+as attribution in derived works.
+
+Some concepts were based on sample F# code that was written by Ralf Herbrich
+Copyright (c) 2007, 2008 Microsoft Research Ltd, available at
+http://blogs.technet.com/apg/archive/2008/06/16/trueskill-in-f.aspx
+
+This PHP code was ported from the C# Moserware.Skills project at 
+http://github.com/moserware/Skills
+
+Both the PHP code in this PHPSkills project and C# in Moserware.Skills are
+Copyright (c) 2010 Jeff Moser <jeff@moserware.com>
+
+Redistribution and use in source and binary forms, with or without modification, are
+permitted provided that the following conditions are met:
+
+   1. Redistributions of source code must retain the above copyright notice, this list of
+      conditions and the following disclaimer.
+
+   2. Redistributions in binary form must reproduce the above copyright notice, this list
+      of conditions and the following disclaimer in the documentation and/or other materials
+      provided with the distribution.
+
+THIS SOFTWARE IS PROVIDED BY JEFF MOSER ``AS IS'' AND ANY EXPRESS OR IMPLIED
+WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL JEFF MOSER OR
+CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+The views and conclusions contained in the software and documentation are those of the
+authors and should not be interpreted as representing official policies, either expressed
+or implied, of Jeff Moser.