TIGRE v2.0

This new release of TIGRE contains:

• Varian and Nikon scanner data loaders.
• Python 2 and 3 support in both Linux and Windows
• Multi-GPU is now efficiently supported in python
• Better support for 2D tomography
• FDK detector offset support (wang weights)
• FISTA proximal algorithm added (with TV-proximal)
• Dozens of bug fixes and minor improvements