Rearranged some things and added the visibility.m4 macros. Started to lay the

Rearranged some things and added the visibility.m4 macros. Started to lay the
groundwork for being able to turn on -fvisibility=hidden, which in this lib
will likely be a nice speed win. (At these speeds, the extra mem access might
even be noticed)
Moved code that was commented to only be private to private headers. Removed
the need for installation of any of the private headers.