Add support for the ESP32.

Eliminate static data when unreferenced

Updating the driver lib refs to point to current latest versions.
There is one driver still remaining, as it's PR has not been
merged yet (Avnet/wnc14a2a-driver#10).

Merge pull request #106 from ARMmbed/shared_queue_single_thread

Change Easy Connect to support single thread application

ESP8266 v1.5

Change - ESP8266 now clears socket buffer packets on reset and close 
- this resolves DNS issues visible with Cloud Client aka
- "Cloud Client failing to reconnect after update registration due to DNS error"

.gitignore - add missing folders

Wifi-ISM43362, wnc14a2a-driver, and WizFi310 were missing from .gitignore.

Update Wifi-X-Nucleo

Lots of changes, easy-connect was way behind.

```
376b457 (HEAD -> master, origin/master, origin/HEAD) Merge branch 'betzw_wb'
708b8df Add "Known limitations" section to `README.md`
b8348c5 Merge branch 'betzw_wb'
8b10163 Return error when trying to receive from not yet connected socket
4e3d883 Merge branch 'betzw_wb'
629cf6c Adapt `SPWFSAxx::_process_winds()` to latest version of `ATCmdParser::process_oob()`
ee43a66 Add more debug messages to `SPWFSAxx::send()` and make these more accurate
2f9a51d Align timeout values
8482339 Merge branch 'betzw_wb'
38bcfc2 Optimize oob order
28bf31a Trial to work around module API bug regarding socket closing
3a441a9 Harmonize disconnection handling
35fc005 Make debug message output conditional
97454d0 Pretend that callers to `SPWFSAxx::close(int spwf_id)` pass a valid `spwf_id`
80bad08 Merge branch 'master' into betzw_wb
790d876 Merge branch 'betzw_spwfxx_debug_wb' into betzw_wb
0fe59e4 Speed up socket closing
15026ec Merge branch 'betzw_spwfxx_debug_wb'
d25ad39 Handle potential connection losses while sending data
0cea621 Merge branch 'betzw_spwfxx_debug_wb'
727825a Improve performance of AP scanning
b1c6d92 Merge branch 'betzw_wb'
dd283a9 Merge branch 'betzw_spwfxx_debug_wb' into betzw_wb
24689f4 Remove incorrect assert from `SPWFSAxx::_network_lost_handler_bh(void)`
198f893 Merge branch 'betzw_wb'
e80d047 Merge branch 'betzw_spwfxx_debug_wb' into betzw_wb
d75cf4d Remove incorrect assertion
3e800e5 Merge branch 'betzw_wb'
d854524 Merge branch 'betzw_spwfxx_debug_wb' into betzw_wb
031246f Correct clearing condition for pending data
8676c59 Fix bug ignoring `_read_len()` error return code
b303052 Improve credential handling
6500cd9 Merge pull request #10 from juhaylinen/empty-strings
8877938 Merge branch 'betzw_spwfxx_debug_wb' into betzw_wb
8906deb Make blocking event callback recursive
599765e Improve credential handling
16ec811 Slight comment improvements
e567dff Merge branch 'betzw_spwfxx_debug_wb' into betzw_wb
a388741 Revert "Make blocking event callback recursive"
c321b78 Extend number of critical module operations with (external) callback blocking
d24c1a0 (tag: v1.1.1) Merge branch 'betzw_spwfxx_debug_wb' into betzw_wb
ab117ca Do not call the (external) callback in IRQ context while performing critical module operations
9f5c640 Make blocking event callback recursive
69594a7 Allow to ignore failures in switching off WINDs
974ecf7 (tag: v1.1.0) Merge branch 'betzw_spwfxx_debug_wb' into betzw_wb
67f6137 Enable `SPWFSAxx` synchronization & disable WINDs where necessary
ac0c5e2 Add oob handling for "+WIND:24:WiFi Up::"
a890144 Split up big packages in smaller ones
4da6ac6 Make `_recv_ap()` timeouts reasonable
b7ac561 Merge branch 'betzw_backup_wb' into betzw_scan_wb
3fa0285 Add Grosgrain Synchronization & Asynchronous Indications Based Receiving
f7f0ed7 Backup commit
8775850 Typos
c1d9d3d Use less debug messages
```

ESP8266 driver update

Get in fix for;
- fix_would_block_causing_disconnect

Update wnc14a2a-driver.lib (#93)

moved PIN definitions to mbed_lib.json rather than hard-coded in source file
Move Arduino-pin defines to header

README - stress test link

Add link to the stress test, network stack developers really need
to know about it and run the tests with it as well.

Merge pull request #82 from ARMmbed/esp8266_update

Update ESP8266 driver with bugfixes and new features