Rework the load_nif mf:Mod:Fn option
Rework the load_nif mf:Mod:Fn option

It turned out the module calling erlang:load_nif/2 must match exactly
the module in the specified in the NIF. Thus can't go via any another
module. The call to erlang:load_nif/2 must be _in_ the generated
module.

So add a substitution option to make the code generator change
special (verbatim) terms {{nifbase}} and {{loadinfo}} into the actual
nif code file basename (sans .so) and load info (version).

olgeni/gpb,mmmries/gpb