doc: avoid long lines in input and output, indexing fixes.

doc: avoid long lines in input and output, indexing fixes.

* doc/libtool.texi (Linking libraries)
(Module loaders for libltdl): Manually line-wrap examples, to
avoid long lines.
(Libltdl interface, User defined module data)
(Module loaders for libltdl): Wrap long @deftypefun input lines
using trailing '@'.  Use @deftypefun rather than @deftp where
appropriate, and add spaces in @deftypefun lines to fix the
index entries generated from these lines.
(Cheap tricks): Use @smallexample rather than @example, to avoid
long lines.

Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>