Support Modem Sleep

[TheButlah]

Esp-idf supports modem sleep, where the wifi can still maintain a connection to the AP but sleep while there is no network activity, saving power. Could something like that be supported in the current async esp-wifi?

[bjoernQ]

We already have the ps-min-modem feature which reduces power-consumption.
We should probably check what it will take to support ps-max-modem as well

[TheButlah]

Oh, I didn't see that! Its been a while since I've updated my version, it probably was added recently. Could that feature be added to the features table in the README with a quick description of what it does/how it works?

[bjoernQ]

Thanks for mentioning it's not in the README - we'll definitely address this before the (soon to happen) first release on crates.io

[bjoernQ]

Added ps-max-modem in #273