Add custom extension builder to setup.py
Add custom extension builder to setup.py

Fixes #358

In order to provide a more stable installtion accross different packages
managers, the deduction of the build_lib directory have been removed and
replaced by the usage of a custom extension builder which is guaranteed
to know the exact path to the temporary build directories.

blue-yonder/turbodbc,blue-yonder/turbodbc,blue-yonder/turbodbc,blue-yonder/turbodbc