GitLab

Found by Coverity Scan.

- platform layer currently broken (not adapted yet)
- memmory_buffer_alloc too

Makes it clearer that the user is not supposed to include them

A simple execution of tmp/invoke-rename.pl

Note from future self: actually md_init_ctx will be re-introduced with the
same signature later, and a new function with the additional argument will be
added.

- more freedom for us to change it in the future
- enforces hygiene
- performance impact of making accessors no longer inline should really be
  negligible

The SHA4 name was not clear with regards to the new SHA-3 standard. So
SHA2 and SHA4 have been renamed to better represent what they are:
SHA256 and SHA512 modules.

process functions

Access to process functions is needed to reduce possible timing attacks
on SSL MAC checks. As SSL is set to move to using the dynamic MD layer,
the MD layer needs access to these process functions as well.