change project name from UnixHostDuino to EpoxyDuino

[bxparks]

I'm going to change the name of this project to EpoxyDuino to preemptively avoid any future trademark issues with the word "Unix". I think the 3 big user-visible changes are:

• The repo will be renamed. GitHub says (https://docs.github.com/en/github/administering-a-repository/renaming-a-repository) that it will install a redirect under the old name.
• The cpp macro EPOXY_DUINO will replace UNIX_HOST_DUINO macro, but the latter will be kept for some time for backwards compatibility.
• A new EpoxyDuino.mk file will replace UnixHostDuino.mk, but I will point the old file to the new file for backwards compatibility.

Initially, I didn't think that this project would become as useful as it has. I like self-descriptive names for projects, and at the time, UnixHostDuino seemed the most self-descriptive. But I have since found that I want to build other things on top of this project, so it seems best to avoid any potential legal problems.

"Epoxy" is a generic word, there is no trademark. It kinda sounds like "Posix-y" or "Unix-y". And it describes 2 materials that combine to make something stronger. This seems like an appropriate metaphor for this project that implements the Arduino API on Posix-y or Unix-like desktop class machines.