Move mongoose docs to https://cesanta.com/docs/

PUBLISHED_FROM=ebf5568abe82952ab2751298185a10189098013f

docs/overview/usage-example.md

@@ -1,6 +1,4 @@
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-title: Example - TCP echo server
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+# Example - TCP echo server
 
 - Copy `mongoose.c` and `mongoose.h` to your build tree
 - Write code that uses the Mongoose API, e.g. in `my_app.c`