Update README.md

Mentioned crash when MGet[]ting classes
Throw/Catch to exit error in MEvaluate
Merge branch 'cdev' into mma-dev
Merge branch 'develop' of https://github.com/rsmenon/MATLink into cdev
Merge branch 'mma-dev' of https://github.com/rsmenon/MATLink into cdev
Prompt for MATLAB directory