ESP8266 SDK Core 2.3.0 compat

[OttoWinter]

Description:

Adds basic support for core SDK core 2.3.0 for ESP8266. Some components will likely give compile errors, but I certainly won't backport them (huge pain).

These things won' work:

• everything that uses pin interrupts (uart, pulse counter, duty cycle, rotary encoder, remote receiver)
• neopixelbus
• PWM

Expect other things to break too, I don't consider 2.3.0 officially supported.

Related issue (if applicable): fixes esphome/issues#145

Pull request in esphome with python changes (if applicable): esphome/esphome#
Pull request in esphome-docs with documentation (if applicable): esphome/esphome-docs#

Checklist:

• The code change is tested and works locally.
• The code change follows the standards

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in esphome-docs.