Merge branch 'master' into master

Author: krzychb

.gitignore

@@ -5,3 +5,6 @@ tools/esptool/
 tools/mkspiffs/
 package/versions/
 exclude.txt
+tools/sdk/lib/liblwip_src.a
+tools/sdk/lwip/src/build
+tools/sdk/lwip/src/liblwip_src.a

README.md

@@ -34,12 +34,12 @@ If you find this forum or the ESP8266 Boards Manager package useful, please cons
 ##### Stable version ![](http://arduino.esp8266.com/stable/badge.svg)
 Boards manager link: `http://arduino.esp8266.com/stable/package_esp8266com_index.json`
 
-Documentation: [http://esp8266.github.io/Arduino/versions/2.1.0/](http://esp8266.github.io/Arduino/versions/2.1.0/)
+Documentation: [http://esp8266.github.io/Arduino/versions/2.2.0/](http://esp8266.github.io/Arduino/versions/2.2.0/)
 
 ##### Staging version ![](http://arduino.esp8266.com/staging/badge.svg)
 Boards manager link: `http://arduino.esp8266.com/staging/package_esp8266com_index.json`
 
-Documentation: [http://esp8266.github.io/Arduino/versions/2.1.0-rc2/](http://esp8266.github.io/Arduino/versions/2.1.0-rc2/)
+Documentation: [http://esp8266.github.io/Arduino/versions/2.2.0-rc1/](http://esp8266.github.io/Arduino/versions/2.2.0-rc1/)
 
 ### Using git version
 [![Linux build status](https://travis-ci.org/esp8266/Arduino.svg)](https://travis-ci.org/esp8266/Arduino) [![codecov.io](https://codecov.io/github/esp8266/Arduino/coverage.svg?branch=master)](https://codecov.io/github/esp8266/Arduino?branch=master)