Qibo 0.0.1b2

Pre-release for testing.

• multi-gpu support
• single package with cuda10.2 and cpu-only support
• new hamiltonian overloading operators
• decomposition of multi-controlled X gates
• options to set default simulation precision, backend and device
• enhanced interface for gate matrices
• pylint errors fixed
• fixed checks for custom operators

Linux wheels are compiled with CUDA 10.2 support.