Updates for esp8266 platform
Continuations support
Fix continuations
Fix build errors
Implement delay()
Implement global init for esp8266
Tidy up backend code for esp8266 (malloc, free, yield)
Implement digital IO functions
Fix initialisation, fix HardwareSerial, add esptool.py flashing
Remove WiFi shield library
Fix malloc/free references
Move some code to flash and fix prototypes
Add circular buffer implementation
Add ESP8266WiFi library
Don't use timer for zero delay
Modify the linker script to move some code into flash, enable -mtext-section-literals
Open-drain output mode
Implement most WiFi functions

Need to update to SDK 0.9.3 because DHCP client functions are missing
Add stubs for itoa, ltoa
digitalWrite fix