Remove old lingering "float" command

 * This used to be a proposed idea, but it is not necessary in the shlib
   core and has long ago been replaced by the math library.
Rename __shlib_lib_valid to __shlib_valid.

 * Unlike __shlib_lib_resolv and __shlib_doc_resolv, we have no
   alternate "valid" routines, so there is no reason to use this
   excessively long naming.
Some basic cleanups

 * Add hascmd, pathcmd, and pathname to the shlib namespace

 * Unset __shlib_doc and __shlib_doc_resolv when releasing program
   execution control from shlib to whatever program we are executing.
   The doc interfaces are for the cmdline and currently have no purpose
   once we have proceeded further.  Maybe that will change one day, but
   for now we can free memory.
Update some comments
Enhance document mangling
Avoid using namespace aliases w/in shlib core

 * The namespace aliases are by-and-large ment for users of shlib, not
   shlib itself.  Due to the nature of alias expansion, it is best to
   avoid using the aliases.  Further more, we only create aliases for
   interfaces we really want users to use.
Rename pathname to shlib.realpath

 * This interface needs some serious work, but curiously as fragile as
   it appears, it seems to work almost everywhere.
Finished documenting the shlib core