Retarget to4.5

retargeted the main project to 4.5 as this is the minimum it can go due to identity 2.0 only being introduced in 4.5.

I've left the other projects as there are dependencies on SharpArch which is only available as 4.5.1 (you'll probably want to look at that one).

Also made it easier to build the package as it now doesn't require you to set the package restore.

This solves #7