Library Improvements

[oclyke]

These possible improvements came up on the SF forums:
https://forum.sparkfun.com/viewtopic.php?f=83&t=52403&p=213211#p213211

The forum posts also include info on how to change to low power mode

• Add a call to change to low power mode
• Remove 'Wire.begin()' from the 'begin()' call (our new standard is to have users call this themselves so that they may choose things like clock frequency and it doesn't get overwritten by subsequent calls)
• Allow users to specify their own I2C port (Wire, Wire1, Wire2, swWire, etc)

[oclyke]

I've assigned myself b/c the engineer who wrote this is no longer at SF. However I don't have bandwidth to handle it is more of a reminder for the long-term. Hope someone else can hop in and help out!