* Changes for FreeRTOS/LwIP Port for the ESP32 (ESP-IDF)
Adding FreeRTOS/LwIP to compiler:
* adding freertos option
* dyncalls for freertos
* add freertos to posix os list
* adding lwip option
Setting up networking FreeRTOS/LwIP Port:
* setting up lwip network for freertos
* fixing posix / networking for freertos
* disable setInheritable for freerots
* using lwip for net control items
* Fix builds by ignoring lib/posix/posix_freertos_consts.nim similar to lib/posix/posix_other_consts.nim
New issue: since `Table[A, B]` allocates its backing storage with
`newSeq[KeyValuePair[A, B]]`, it's no longer legal to create a table
with `not nil` types used as either keys or values.
- For clarity: Changed the unregister if statement to use the in operator instead of
the set intersection operator in ioselectors_epoll.nim and
ioselectors_select.nim.
- Fixed unregister of Event.User case on the Android branch.
* Added ``getFd`` procedure for retrieving the underlying
selector's FD.
* Selectors module's procedures now accept an ``int`` as well as a
``SocketHandle``.
* ReadyKey now contains the error code for Event.Error events.
* Merge upcoming async with current.
* Various improvements to selectors (mostly docs).
Two changes to highlight:
* Renamed ``setEvent`` to ``trigger``
* Reused setBlocking from nativesockets.
* Various changes/fixes to asyncdispatch after upcoming merge.
* Make some attempts to be compatible with older selectors.
* Reuse epoll module in ioselectors_epoll.
* Fix#5128, #5184.
Removed flush() procedure from ioselectors.nim
Changed methods of work with application-driven data
* Make cache switch for kqueue, update test for it.
* Fix registerProcess bug returns wrong id.
Fix tupcoming_async test to compile with upcoming again.
Change socket() as unique identifier to dup(socket) as unique identifier.
