Achievement unlocked: CC3220 port prints a boot banner.
Then locks up.

Included in this PR is refactoring to pull out common parts to be shared with CC3200.

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Fixed bug in websocket handshake:
now adding Sec-WebSocket-Protocol header in handshake response.

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https://forum.mongoose-os.com/discussion/comment/4620/#Comment_4620

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Ignore all the mess, this is just the beginning...

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Fix headers that didn't have it

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Change the API to heap-allocate the string and get rid of a bunch of fat stack buffers.

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Also allow disabling conmpression and forcing server cipher list.

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Write unit tests for some mg_str functions.

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h/t @hendrikw01

Fixes https://github.com/cesanta/mongoose/issues/826
Closes https://github.com/cesanta/mongoose/pull/831

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Also amend api_net.js to use returned length.

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Raised in previous commit by mistake

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As required by the LWIP API

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With different filesystem implementations and storage drivers, like grown-ups have :)
This is not currently used to add any new functionality, we still have
only one FS and driver on ESP8266 and ESP32; CC3200 has two: SPIFFS and SLFS.
This will be used soon to implement filesystems on additional SPI flash chips and SD cards.

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 - Move keep alive management up to the Mongoose library
 - Only outgoing control messgaes should reset keepalive timer
 - Add unit test

https://forum.mongoose-os.com/discussion/1155/mqtt-keep-alive-compliance-issue

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