add start of documentation for second and third prototypes and matching picture

doc/TinySpHEAR_zapnspark.md

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+# The *SpHEAR Project
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+## TinySpHEAR with Zapnspark interfaces
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+The TinySpHEAR microphone is a traditional 4 capsule tetrahedral first order Ambisonics microphone. This improved design adds four printed circuit boards with Zapnspark phantom power interfaces housed in the microphone body. A trailing cable ends in four XLR connectors. 
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+The picture shows the full design as previewed in OpenSCAD and a picture of the second prototype (built with Primo EM182 10mm capsules, 9.6mm microphone radius). 
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+<img src="pictures/TinySpHEAR_zapnspark.png" width="400">
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+The 3D models also include a shock mount that clips into a standard microphone stand mount.
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+The two main model files are tuned for ![EM182](TinySpHEAR_EM182.scad) (10mm) and ![EM200](TinySpHEAR_RM200.scad) (14mm) capsules. Uncomment the different "render_" lines to render different parts or the complete microphone assembly. 
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