Add AP start/stop events

[jpasqua]

Add two new values to wifi_config_event_t: WIFI_CONFIG_AP_START and WIFI_CONFIG_AP_STOP

When wifi_config_init2() is used and the client has provided a callback, it will be invoked when the library enters and exits AP mode. This allows the client to give the user some sort of feedback (e.g. blink an LED) that an action needs to be taken.

[maximkulkin]

Could you change commit title to "Add AP start/stop events".

Also, usually things like .DS_Store, your IDE files or environment related things is better to have in machine global .gitignore: just create .gitignore in your home directory and then run git config --global core.excludesfile '~/.gitignore'

[jpasqua]

Title changed. Agreed on .gitignore. Do you want me to do something about it w.r.t. this pull request, or will you just not integrate it?

[maximkulkin]

I think we can remove that commit. Otherwise LGTM. Thank you

[maximkulkin]

Title changed

@jpasqua Oh, that's not what I meant. I mean, change title of that particular commit, not the title of PR. I still see commit saying "Add additional event types" which might be confusing to see in the history in the long run.

[jpasqua]

Let me know if this looks OK now. I've been using my forked version and forgot about this PR.