Merge remote-tracking branch 'Dev/master' into release-candidate

[v1.18.2.r7] Firmware release

### New Features
- Esp32 touchpad functionality exposed to micropy

### Improvements
- Added RSA signature generation API to moducrypto
- Added support for saving strings in NVS - PR pycom#226 , author: @psychogenic
- LTE class refactoring

### Bug Fix
- Fix UART.sendbreak not defaulting to 13 bits as suggested by Documentation Issue pycom#280

[v1.18.2.r6] Firmware release

### Bug Fix
- Updated LTE class to fix issue in modem FW version detection.

Merge remote-tracking branch 'iwahdan/master'

[v1.20.0.rc10] Release Candidate

Increased LoRa timer task Stack Size

[v1.20.0.rc9] Firmware release candidate

### Improvements:
- Releasing GIL when ssl handshake is performed.
- Allow PDN list update when carrier is defined in LTE
- Add support for LTE modem responses greater than UART buff size
- Added Check for LTE band support against both SW and HW versions of the LTE modem.
- Updated Sqns upgrade scripts to v1.2.5
### Bug Fixes:
- Enabling Access to 2nd SPI perf for GPY modules
- Use Hardware timers for Lora timer tick to fix RTOS timer drifts when cache is disabled.
- Updated OTA fixing failing OTAs after switching to Factory Partition.
- Fix crash when pin ISR handler fires (i.e. LoRa TX done) during flash operation PR pycom#278 by Martijn Thé  @martijnthe
- Remove defaulting of wifi max_tx_pwr  to level 20 in init()
- modlora: Reverted the rx spread factor in stats

[v1.18.2.r4] Firmware release

### Improvements:
- Releasing GIL when ssl handshake is performed.
- Allow PDN list update when carrier is defined in LTE
- Add support for LTE modem responses greater than UART buff size
- Added Check for LTE band support against both SW and HW versions of the LTE modem.
- Updated Sqns upgrade scripts to v1.2.5
### Bug Fixes:
- Enabling Access to 2nd SPI perf for GPY modules
- Use Hardware timers for Lora timer tick to fix RTOS timer drifts when cache is disabled.

[Bug Fix] v1.18.2.r3

mods/machspi.c: Fix for pyb_transfer sending 0x55 always when data buffer is passed. pycom#245

Merge pull request pycom#277 from pycom/stable_r2_update

Merge pull request pycom#276 from pycom/rc8_update