Support LibreSSL by its version output

The command-line API for LibreSSL is currently identical to OpenSSL
1.0.1.  This support is implemented in a case so any future version
distinctions can key off the features in the available implementation.

Such feature-specific support may become more important during the 3.1
development cycle where 0.9.x OpenSSL cannot handle newer features.

Signed-off-by: Josh Cepek <josh.cepek@usa.net>
Fixes: #48