Initial commit for ADC testing.  Doesn't work reliably yet.
Cleaned up ADC code and corrected ADC clock source and acquisition time settings.
Updated slave I2C address to 0x4F
Corrected call to i2c_configure_slave() to pass 0x9E, which configures for address 0x4F (the lowest bit is the read/write bit so it isn't part of the address).  Also removed other I2C initialization code that was not being used.
Added initial code for reporting ADC data over I2C.
Updated ADC driver to store the latest ADC conversion internally.  Access it with adc_read().
ADC conversions are now started immediately after the previous conversion value is received in adc_lthread().  This should maximize the sample rate.
ADC data is now available as a full 2-byte register or as two 1-byte registers (one for the low byte and one for the high byte).
Removed RB0 debug output for ADC.