Fixed compiling with ESP32 + bug fix

[FStefanni]

Hi,

this pr is a small fix for compiling with ESP32. Fixes #136

Moreover, this pr fixes the default behavior for Connection header. Please see https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Connection

Regards

[sachaw]

@fhessel any chance we could please get this merged?

[sekarpdkt]

+1 for early merge

[jackjansen]

@fhessel I don't feel confident enough to review the keepalive change (which I don't understand). But +1 on the sha-header change. I have a merge request ready also for esp32_https_server_compat that is waiting for this merge request...