Add placeholders for the I2C mux and temp sensor classes
Begin developing temperature sensor abstractions

spi_test is temporarily disabled because we are not communicating with
the FPGA
Mux switching now abstracted into temp sensor object
nickname not necessary for I2C mux and temp sensor
Begin abstraction of FPGA
Add Kerrigan class, an FPGA instrument
Update documentation
Merge branch 'feature-temp-sensor' into develop