Idf4 upgrade

[phatpaul]

This is my attempt at finally getting this project to work for me on IDF 4.x (since IDF v3 is now EOL). I'm also upgrading espfs to v3. This includes PR #31 but undoes the rename folder html->espfs.

This will officially drop support for legacy make build and IDF v3 and ESP8266.

This is a WIP:

• [x] tcpip_adapter -> esp_netif
• [x] Ethernet init updated from latest example
• [x] esp_event handlers API changed
• [x] espfs upgraded to v3 https://github.com/jkent/frogfs/releases/tag/v3.0.0 I had to disable preprocessing b/c broken on windows. (Files served via http are empty 0B.)
• [x] Merge https://github.com/chmorgan/libesphttpd/pull/99 which allows espfs v3 to work with libesphttpd
• [x] cleanup