Porting HPKE
This merge request ports the necessary hpke files from the npocs:hpke repository and includes refactoring changes.
- Added required files from nettle:hpke(npocs) into /lib/nettle/hpke
- Created new files "hpke-gmp.h" and "hpke-gmp.c"
- Replaced "gmp-glue.h" with "hpke-gmp.h"
- Removed unused var 't' hpke-hkdf.c:54
- Resurrected nettle-alloca.h
- Modified hpke-hkdf.c to use "ecc_scalar_set()"
- Modified devel/indent-gnutls to ignore nettle/hpke
Edited by Ajit Singh