Feature app core

[YonasJ]

A couple of changes I hope you can add to your active trunk.

1. I updated your gpio file so that open drain pins have the ability to read and write, and I model that in the bitbang.rs example I added.
2. I added a struct called "Console" that I use to do safe(?) println! from the examples. I demo this in the example hello.rs
3. I added an example called button that shows using GPIO for input.
4. I added a file called "watchdog_disabler" which I use to cleanly disable the watchdog in the examples.

It's probably not perfect, as I am still learning rust, but it's a step in the right direction.

Once I figure out how to implement an interrupt handler on GPIO change, I should be ready to roll for the app I am working on.

[arjanmels]

@YonasJ Thanks for contributing. I think this pull request should go directly to the esp-rs/esp-hal repo and not my fork of it. Because then we still need to get this fork merged.

You have some nice examples. (I personally hesitate if your console.rs and watchdog_disable should go into the esp32-hal: they are higher level and specific.)