Implement forward-search for View command on TeX-region.

* tex.el (TeX-evince-sync-view): Use line/col information from the
TeX-region buffer if the View command is made on a region.

* tex-buf.el (TeX-region-create): Position point in the same
line/col as in the original buffer to make forward search work.
Implement LaTeX-command-section.

* style/book.el ("book"): Set LaTeX-largest-level to part instead
of chapter.

* tex-buf.el (LaTeX-command-section-level): New variable.
(LaTeX-command-section-level): New function.
(LaTeX-command-section-change-level, LaTeX-command-section): New
commands.

* latex.el (LaTeX-mode-map): Bind C-c C-z to LaTeX-command-section
and C-c M-z to LaTeX-command-section-change-level.
Document LaTeX-command-section.

* doc/auctex.texi (Starting a Command): Document
LaTeX-command-section and friends.
Move preview/ to top-level.

* configure.ac: Merge from preview/configure.ac.

* .gitignore: Merge from preview/.gitignore.

* autogen.sh: Don't run autoconf in the preview direcotry.

* Makefile.in (subdirs): Remove.
(DESCEND): Remove.
(EXCLUDEDFILES): Remove 'preview/' prefix.
(preview-ball): Likewise and decrement stip-components in tar.
(previewstartfile): Adapt from preview/Makefile.in.
(PREVIEW_AUTOLOAD): Likewise.
(texmf): Likewise.
(preview-latex.el): Likewise.
(latex/Makefile): Likewise.
(auto.el): Likewise.
(install-startup): Likewise.
(install-texmf): Likewise.
(release-commit): Likewise.
(DISTCLEANFILES): Likewise.
(CLEANFILES): Add preview files.
(install-el): Likewise.
(install-lisp): Likewise.
(all): Add texmf dependency and remove DESCEND.
(clean): Remove DESCEND action.
(distclean): Likewise.
(maintainer-clean): Likewise.

* doc/Makefile.in (preview-dtxdoc.texi): Update path of
preview.dtx.

* preview/ChangeLog: Move to ChangeLog-preview

* preview/ChangeLog.1: Move to ChangeLog.1-preview

* preview/auto.el.in: Move to top-level.

* preview/circ.tex: Move to top-level.

* preview/preview.el.in: Move to top-level.

* preview/*.el: Move to top-level.

* preview/images/: Move to images/.

* preview/latex/: Move to latex/.

* preview/Makefile.in: Remove.

* preview/configure.ac: Remove.

* preview/.gitignore: Remove.

* preview/COPYING: Remove.

Signed-off-by: Mosè Giordano <mose@gnu.org>
Make second argument of LaTeX-label optional.

* latex.el (LaTeX-label-alist): Expand doc string.
(LaTeX-label): Make second argument optional to restore backward
compatibility and update doc string accordingly.  (Bug#19178)