This is a bit more consistent with the naming of the other header files
(openlibm_complex.h and openlibm_fenv.h). Re-add an openlibm.h header
that includes all of the public headers as a shorthand.
Fix up all of the source files to include <openlibm_math.h> instead of
<openlibm.h>. While there, fix ordering of the includes.
A couple of small issues still remain with linking:
LINK all
/usr/bin/ranlib: file: libopenlibm.a(e_rem_pio2.o) has no symbols
/usr/bin/ranlib: file: libopenlibm.a(e_rem_pio2f.o) has no symbols
/usr/bin/ranlib: file: libopenlibm.a(k_cosf.o) has no symbols
/usr/bin/ranlib: file: libopenlibm.a(k_sinf.o) has no symbols
/usr/bin/ranlib: file: libopenlibm.a(k_tanf.o) has no symbols
LINK all
ld: duplicate symbol ___ieee754_rem_pio2 in src/s_sin.o and src/s_cos.o for architecture x86_64
collect2: ld returned 1 exit status
