OSSL_PARAM helper functions.

Provide a number of functions to allow parameters to be set and
retrieved in a type safe manner.  Functions are provided for many
integral types plus double, BIGNUM, UTF8 strings and OCTET strings.

All of the integer functions will widen the parameter data as
required.  This permits a degree of malleability in the parameter
definition.  For example a type can be changed from a thirty two bit
integer to a sixty four bit one without changing application code.
Only four and eight byte integral sizes are supported here.

A pair of real functions are available for doubles.

A pair of functions is available for BIGNUMs.  These accept any sized
unsigned integer input and convert to/from a BIGNUM.

For each OCTET and UTF8 strings, four functions are defined.  This
provide get and set functionality for string and for pointers to
strings.  The latter avoiding copies but have other inherent risks.

Finally, some utility macros and functions are defined to allow
OSSL_PARAM definition arr...