In hmac.c rev. 1.13 2018/02/17 14:53:59, jsing@ provided HMAC_CTX_new(3),

In hmac.c rev. 1.13 2018/02/17 14:53:59, jsing@ provided HMAC_CTX_new(3),
HMAC_CTX_free(3), HMAC_CTX_reset(3), and HMAC_CTX_get_md(3).
Merge the documentation from OpenSSL, with many tweaks by me.
Also include a few earlier improvements from OpenSSL.

While here, improve the order of the functions, the description of
deprecated functions, and remove a confusing warning about the
behaviour of HMAC_Init(3) in historical versions of OpenSSL.