Implement AEAD-ChaCha20-Poly1305.

This implementation is based off the description in RFC 7539.

The ChaCha20 code is also updated to provide a means of generating
keystream blocks with arbitrary counter values. This is used to
generated the one-time Poly1305 key in the AEAD construction.
diff --git a/library/Makefile b/library/Makefile
index 5fd693b..de4bd5c 100644
--- a/library/Makefile
+++ b/library/Makefile
@@ -47,7 +47,8 @@
 DLEXT=dll
 endif
 
-OBJS_CRYPTO=	aes.o		aesni.o		arc4.o		\
+OBJS_CRYPTO=	aead_chacha20_poly1305.o	\
+		aes.o		aesni.o		arc4.o		\
 		asn1parse.o	asn1write.o	base64.o	\
 		bignum.o	blowfish.o	camellia.o	\
 		ccm.o		chacha20.o			\