portable Directory Reference

Files
	portable_aes128gcm.cpp
	AES-128-GCM and the AES-128 block in software - the backend for a target with no accelerated AEAD.
	portable_aesgcm.cpp
	AES-256-GCM in software - the backend for a target with no accelerated AEAD.
	portable_bignum.cpp
	Software Montgomery modexp - the bignum backend for a vendor with no accelerator.
	portable_platform.cpp
	Platform answers for a target with no RTOS concept of a task - host builds included.