Simple measurment of resistance with microcontroller
Use a voltage controlled precision current source to feed a known current into the resistor. If the measured reading is either too low or too high, adjust the current source to be more appropriate. Take several readings and average.... Maybe 50 readings to counter the lack of bits in your ADC . 

For high valus of resistance you will need to buffer the signal to the ADC with a unity gain opamp circuit because the ADC's input is quite low impedance.

The current source can be built using a DAC to set the demand. It'll need two transistors and two opamps for maximum flexibility. 

You may think this is too complex but if you change your mind let me know. It is a decent method I might add.