The new function |CRYPTO_chacha_96_bit_nonce_from_64_bit_nonce| can be
used to adapt code from that uses 64 bit nonces, in a way that is
compatible with the old semantics.

Change-Id: I83d5b2d482e006e82982f58c9f981e8078c3e1b0
Reviewed-on: https://boringssl-review.googlesource.com/6100
Reviewed-by: Adam Langley <alangley@gmail.com>

poly1305.h was missing exports. While here, chacha.h should also be exported.

Change-Id: I5da9c953d3e5a5ef76a3e96bc4794192abee3ae6
Reviewed-on: https://boringssl-review.googlesource.com/5420
Reviewed-by: Adam Langley <agl@google.com>

Previously, public headers lived next to the respective code and there
were symlinks from include/openssl to them.

This doesn't work on Windows.

This change moves the headers to live in include/openssl. In cases where
some symlinks pointed to the same header, I've added a file that just
includes the intended target. These cases are all for backwards-compat.

Change-Id: I6e285b74caf621c644b5168a4877db226b07fd92
Reviewed-on: https://boringssl-review.googlesource.com/1180
Reviewed-by: David Benjamin <davidben@chromium.org>
Reviewed-by: Adam Langley <agl@google.com>