Add readme and license

LICENSE

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+Copyright (C) 2017-2018 fincs
+
+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.

README.md

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+# citro2d
+
+**( ͡° ͜ʖ ͡°)**
+
+*Library for drawing 2D graphics using the Nintendo 3DS's PICA200 GPU.*
+
+This library contains optimized routines that allow 3DS homebrew developers to
+develop applications that take full advantage of the GPU to draw 2D graphics.
+The routines in this library have been carefully designed and optimized for
+the purpose of removing bottlenecks and allowing higher GPU throughput.
+
+citro2d uses [citro3d](https://github.com/fincs/citro3d) under the hood to
+talk to the GPU. It is possible to use citro2d on its own, or use it alongside
+citro3d to draw mixed 2D and 3D content.
+
+Features:
+- Lightweight and straightforward API
+- Full doxygen documentation
+- Drawing on any surface (C3D_RenderTarget)
+- Drawing images and sprites (the latter contain state whereas the former don't)
+- Drawing text using the system font
+- Spritesheet/texture atlas support using [tex3ds](https://github.com/mtheall/tex3ds)
+- Scaling, flipping, rotation
+- Drawing untextured triangles and rectangles
+- Per-vertex tinting with configurable blend factor (additive color blending with user specified colors)
+- Flexible and configurable gradients
+- Full-screen fade-out/fade-in transitions (to any color)
+- Concurrent usage of citro2d and citro3d