compat: add macro to map symbol in static build

compat: add macro to map symbol in static build

It was pointed out in my examples that doing shared library symbol versioning by
partitioning symbols to version specific functions (as opposed to leaving the
latest symol version at the base symbol name), neglects to take into account
static builds.  Add a macro to handle that.  If you choose a versioning approach
that uniquely names every version of the symbol, then this macro lets you map
your symbol choice to the base name when building a static library

Also, while I'm at it, since we're documenting this in the guide, take the
abbreviated example out of the header

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
[Thomas: remove remaining part of old example]
Acked-by: Thomas Monjalon <thomas.monjalon@6wind.com>