Add md5 (for HTTP Digest Auth)

Removed typedef.
Renamed HAVE_MD5 to NS_DISABLE_MD5

Subsequent PR will introduce NS_DISABLE_HTTP_AUTH and toggle NS_DISABLE_MD5
when it is defined.

On Tue, Dec 23, 2014 at 4:40 PM, Marko Mikulicic <notifications@github.com>
wrote:
>
> In src/md5.c
> <https://github.com/cesanta/fossa/pull/184#discussion-diff-22222567>:
>
> > + * The algorithm is due to Ron Rivest.  This code was
> > + * written by Colin Plumb in 1993, no copyright is claimed.
> > + * This code is in the public domain; do with it what you wish.
> > + *
> > + * Equivalent code is available from RSA Data Security, Inc.
> > + * This code has been tested against that, and is equivalent,
> > + * except that you don't need to include two pages of legalese
> > + * with every copy.
> > + *
> > + * To compute the message digest of a chunk of bytes, declare an
> > + * MD5Context structure, pass it to MD5Init, call MD5Update as
> > + * needed on buffers full of bytes, and then call MD5Final, which
> > + * will fill a supplied 16-byte array with the digest.
> > + */
> > +
> > +#ifndef HAVE_MD5
>
> Some compilers complain about typedef redefinition:
>
> warning: redefinition of typedef 'foo' is a C11 feature [-Wtypedef-redefinition]
>
> , it would be nice to have our code warning free.
>
> Anyway I guess we should make this module disableable for size reasons,
> and have the auth part of http conditionally enabled on either this or the
> builtin md5 impl.
>
> —
> Reply to this email directly or view it on GitHub
> <https://github.com/cesanta/fossa/pull/184/files#r22222567>.
>