Add min_version and max_version APIs.

Amend the version negotiation tests to test this new spelling of max_version.
min_version will be tested in a follow-up.

Change-Id: Ic4bfcd43bc4e5f951140966f64bb5fd3e2472b01
Reviewed-on: https://boringssl-review.googlesource.com/2583
Reviewed-by: Adam Langley <agl@google.com>