Make BCDDigits chainable

[tekktrik]

Not tested.

Resolves #39 by changing inheritance of BCDDigits to ChainableMAX7219. Also adds a value check to notify if a digit is ever out of range.

[FoamyGuy]

@bschymanski is this new functionality something you have the hardware to test?

[bschymanski]

i will download the new code and will test this with two daisychained MAX7219 hopefully tomorrow

[tekktrik]

I actually ordered something to help with this, but mail is turtle-pace right now, converting to draft in the meantime. I'll re-convert when I get it and finalize this PR.

[tekktrik]

Hardware arrived, now I just need to figure out which moving box has my soldering equipment >:(

[tekktrik]

Pros: I have the prototype working!
Cons: It's not working as intended, chances are this will take me a while!

[FlantasticDan]

@tekktrik Glad to see someone is taking this up, I think you might be in a similar place where I left off. I tried to get chained BCD Digits working after I implemented ChainableMAX7219 in #37 but found that it would require some reworking of the existing BCD implementation I wasn't prepared to undertake.

I have the hardware to test when you're ready or if you need some help!

[tekktrik]

Unfortunately, I think I'm going to close this for now since I haven't had time to work on and don't know when I will. I'll keep the branch though, and hopefully I'll be able to come back to this.