Use libsodium for SHA-2 instead of openssl, vendor MD5/SHA1

This commit partially reverts a6ca68a,
reviving in-tree implementations of MD5 and SHA-1, but not SHA-256.
For SHA-256 and SHA-512, libsodium implementations are used.

Tagging release 2.5.1

Tagging release 2.5.0

Use libsodium for SHA-2 instead of openssl, vendor MD5/SHA1

This commit partially reverts a6ca68a,
reviving in-tree implementations of MD5 and SHA-1, but not SHA-256.
For SHA-256 and SHA-512, libsodium implementations are used.

Make gtest optional by skipping tests in case of --disable-gtest

Tagging release 2.4

Tagging release 2.4pre-rc1

Tagging release 2.3.16

Tagging release 2.3.15

Tagging release 2.3.14