Move source code into src subfolder.

[aentinger]

Hi @facchinm 👋

I've been wondering if there's a need (caused by your builder modifications) for all the source files to be located in the top-level library folder or if they can be safely moved into src subfolder?

[facchinm]

There should be no issue (we need to double check this line https://github.com/bcmi-labs/Arduino_Threads/blob/master/Wire.h#L4 ).
Do you mind testing it with the examples and eventually file a PR now that there's nothing open 😉 ?

[aentinger]

I've created the PR ( #10 ) but my builder is currently broken. I was hoping you could test it 👼 (a compile should be fine)