STYLE: Change source template files to .in extension

STYLE: Change source template files to .in extension

The cblas_mangling_with_flags.h and lapacke_mangling_with_flags.h
are template files that are not used directly.  They need to be
configured (i.e. copied) to lapacke_mangling.h and cblas_mangling.h
header files that are used.  These renamings make the intent of
these files more clearly reported.

The file LAPACKE/include/lapacke_mangling.h should not be stored in the
repository because it should be generated (copied from above) at build
time.