Update README.md

I thought it might be best to add a few more dependencies to the example script as these do not come installed by default. Also added a link to the AMD GPU version.

Unify and parameterize CryptoNight functions

Update static flags to fix seg fault

-static will compile, but causes a segment fault on both build and target. Using the new flags compiles cleanly and runs on both build and target. (Build = debian sid [test], Target= debian jessie [stable])

Adding Common Issues section.

Most of this is taken from forum or from config.txt (and added new one for Windows 7 Home computers).  Consolidating information here.