Rename all instances of "board" to "display"

[brettfiedler]

As it says, it's easier to refer to this as the Display and that's how I've been using it and publishing about it. Let's go ahead and rename everything. Let me know if there are any confusing cases.

[jessegreenberg]

I think everything has been renamed. Anything else here @brettfiedler?

[brettfiedler]

Need to also rename the docs website, which I will do. Leaving assigned.

[brettfiedler]

Ran through the doc site and made these changes.