Add new program dhparam and update docs.

Gets Lutz Jaenicke's name right this time :-)

Apologies to both concerned.

minor changes.

Docs haven't been added at this stage. They are probably
best included in the 'ciphers' program docs.

Slightly clarify the RAND_... documentation.

(we're now using fopen(..., "rb+") instead of fopen(..., "wb"),
so the file is not truncated automatically).

just return -1 as in other error cases.

serial numbers.

could rename too :-(

has s/mime functionality.

benefit of MS-DOS users.

non-function pointers to function pointers and vice versa.
The current solution is to have unions that describe the
conversion we want to do, and gives us the ability to extract
the type of data we want.

The current solution is a quick fix, and can probably be made
in a more general or elegant way.

((void *)0), by have a 0 instead.