MCP23017 some features not working since 2018

[gen2thomas]

I'm trying to implement a driver for Adafruit RGB Positive 16x2 LCD+Keypad Kit for Raspberry Pi.
Therefore I started writing a wrapper around MCP23017 (port expander) and HD44780 (LCD driver).

Unfortunately the MCP driver lost some features with this commit:

• SetPullUp() not working anymore
• SetGPIOPolarity() not working anymore

Although the originated problem was caused only by a small bug in the read function, there was a huge change done in the write function, which was responsible to set or clear bit in the read register and write the new value, which was perfect before. This old behavior can be seen by the incomplete cleanup in the parameters of write() - the parameter "pin" is not used anymore.

Also the subsequent commit has only fixed new problems, introduced by the first commit.

I will start with re-insert the old lines at write function and try to improve the unit tests to reflect the problem.