I2C / Wire not reliable

after the other Wire/i2c issues have been closed ( #166 etc), and the speed got better, some I2C devices started working with the 101.

However, it's still far from _really_ working. Basically, in practice I2C is not usable on the 101 - it's slow, unreliable. Code / hardware that works with _all_ other Arduinos, does not work with the 101.

I have multiple I2C devices here which work on _all_ official Arduinos, except the 101.

BTW I'm using the latest code from this repo.

We're the manufacturer of the Tentacle Shields, these are isolation shields for sensor circuits made by Atlas Scientific. E.g. the pH sensor circuit: https://www.atlas-scientific.com/_files/_datasheets/_circuit/pH_EZO_datasheet.pdf

Schematics of the shield mentioned above is here: https://github.com/whitebox-labs/tentacle-mini-oshw/blob/master/hardware/T2_mini_schematic.pdf

@bigdinotech your fix did help somewhat, but unfortunately Wire is still unreliable. If someone's working on this, I can send i2c devices to test, if needed.

Start by reviewing the related Wire/I2C issues, including #166, and reproduce the behavior with the affected I2C devices and Tentacle Shield described in the issue. Use the linked shield schematic and compare behavior with official Arduinos; done means the same devices work reliably and at a usable speed on the 101.

Written by the indexing model from the issue text.