Encapsulate buffer management into PixelBuf.

[tannewt]

Also provide show() and fill() on the super class.

This is compatible with the previous PixelBuf API by accepting buf and
rawbuf in the constructor, allowing show() to be shadowed and providing
fill at the top level.

Libraries should not release based on the new API until the built-in _pixelbuf is also updated.

[caternuson]

Looks good.

I also did a local update of NeoPixel_SPI based on these changes to test it out. Works as expected. I did not test anything related to DotStar.

I'll let you deal with the linter in whatever way best suits you. :)

[caternuson]

Not part of your PR, but made me look - what's the purpose of called in the example?

[tannewt]

@caternuson It's there to ensure that _transfer is called by the PixelBuf implementation. It is a bit tricky to do in the native code.

[tannewt]

@dunkmann00 Just realized I had done this too. Anything here that would be interesting to move into your code?

[dunkmann00]

I actually noticed this this morning...really wish I had checked the pull requests before I made one, could've definitely saved myself some time!

Our changes were very similar, the one thing we went about differently was you used a memoryview to handle separating the color data from the header/footer in the buffer. I used the code that was there, which just stored the offset value and always performed the operations taking that into account.

So, if you prefer the use of the memoryview I could change that, but otherwise it looks like we both had very similar end products.

[tannewt]

@dunkmann00 Either way is fine for me. Thanks again for picking this up!