build: Build and install libtextstyle.
* autogen.sh: Recurse into libtextstyle directory.
* configure.ac: Likewise.
* Makefile.am (SUBDIRS): Add libtextstyle.
* DEPENDENCIES: Mention that libiconv and ncurses are also used by libtextstyle.
* PACKAGING: Recommend to ship libtextstyle as a third binary package.
* NEWS: Mention that libtextstyle is installed.
