Fix ":param:" syntax in KDF docs
Trun off linkcheck, it's too noisy. Fixes #652
Merge pull request #701 from alex/disable-linkcheck

Trun off linkcheck, it's too noisy. Fixes #652
Merge pull request #700 from wbolster/patch-1

Fix ":param:" syntax in KDF docs
Use buffer of EVP_MAX_MD_SIZE bytes for digests

OpenSSL doesn't actually guarantee to only write to digest_size worth of
bytes in the output buffer. The examples and docs claim this constant is
the max.