revamp include mechanism; update copyright; fix for OSX

Makefile.am

c_utils/c_utils.c

c_utils/c_utils.h

c_utils/memusage.c

c_utils/memusage.h

c_utils/walltime_c.c

c_utils/walltime_c.h

configure.ac

libsharp/sharp.c

libsharp/sharp.h

libsharp/sharp_almhelpers.c

libsharp/sharp_almhelpers.h

libsharp/sharp_core.c

libsharp/sharp_core_inc.c

libsharp/sharp_cxx.h

libsharp/sharp_geomhelpers.c

libsharp/sharp_geomhelpers.h

libsharp/sharp_internal.h

libsharp/sharp_legendre_roots.c

libsharp/sharp_legendre_roots.h