Add PNG logo and PostScript source

License: Public Domain
Adapted from: https://www.lua.org/images/
Graphic design by: Alexandre Nakonechnyj

doc/logo/LICENSE

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+Graphic design by Alexandre Nakonechnyj.
+PostScript programming by the Lua team.
+This code is hereby placed in the public domain.
+
+Permission is hereby granted, without written agreement and without license
+or royalty fees, to use, copy, and distribute this logo for any purpose,
+including commercial applications, subject to the following conditions:
+
+* The origin of this logo must not be misrepresented; you must not
+  claim that you drew the original logo. We recommend that you give credit
+  to the graphics designer in all printed matter that includes the logo.
+
+* The only modification you can make is to adapt the orbiting text to
+  your product name.
+
+* The logo can be used in any scale as long as the relative proportions
+  of its elements are maintained.