Added the files spi_2.c and .h to repository and wrote the masks of evry
register that I might use for the development.
+ Added definitions for the different selectors.
+ Added many more function to the API draft.
+ Added a huge comment for an alternative method for selecting many
devices than just 4.
+ added more API function to spi_2.c (this will later be refactored to
spi.c)
+ Commented functions
+ Created a struct for initialization
Added loopback control functions to spi.
Added mask values for some masks.
Added even more values to masks in spi_2.h
Changed spi_settings structure and created a structure for initializing
the selectors (spi_selector-settings).
Wrote comments for two functions of the API in spi_2.h
Commented on many function in spi_2.h
Added a few slave functions in  spi_2.h