Fast channel reads via context manager

[caternuson]

Not perfect, but helps. Proposed fix for #27.

[ladyada]

question - could we 'cache' the config register value, and if the pin has changed, send and if pin has not changed, skip that? then you dont have to have a separate 'fast' flag

[caternuson]

Maybe. I was thinking the current way it works would be preserved. It's not efficient, but works. And if someone just loops on a single channel, nothing special happens. This would be single-shot / "slow". Nice and simple. How it currently works and hopefully should work for most cases.

for i in range(samples):
    data[i] = chan0.value

There are caveats to the fast read, so wanted to make it more explicit that it's being used, i.e. the context manager. This would be continuous / "fast". For more advanced uses.

with chan0 as chan:
    for i in range(samples):
        data[i] = chan.value

So you actually have to turn it on. It doesn't just kick in automagically.

Hmm. Could maybe move the fast parameter to a member variable of ADS1x15 and then turn it on/off with @property style access? Same general idea as what's currently in place, just changing the way it's triggered.

[caternuson]

...but easy enough to try out. @ladyada checkout PR #33 which takes the caching approach.

[caternuson]

Closing this. Going with the approach taken in PR #33 .