The build script was added to obtain the correct values of the
errno C preprocessor definitions. This way no matter what the platform
has defined them as, they will be correct in the libraries code.
This required the fixing of the features section to properly handle
passing on the use_std feature. It also required that the memory functions
were moved to the main library module instead of within the rust module
as was previously desired. The C module then correctly skips defining the
external C library functions.
Basic time functionality was also added.
