Make Tensora work in Windows

[drhagen]

Tensora's use of CFFI does not work in Windows. The following issues need to be fixed:

• Cannot use FFI.dlopen(None) to grab a generic C library because there is no generic C library in Windows. There are several possible solutions.
• Cannot use free as just a generic function because free is not the same function in all Windows libraries. This could be made a unix-specific feature because it is only used by take_ownership_of_tensor, which is not used internally by Tensora.
• Cannot delete the library after loading it because files in use cannot be deleted in Windows