Fix markup.
Avoid compiler warning with recent glibs.

* src/epdfinfo.c (main): Since glib 2.36 g_type_init is deprecated.
Added TODO item.
Avoid redisplay when minibuffer is active.

* lisp/pdf-view.el (pdf-view-maybe-redisplay-resized-windows): Check
  for minibuffer-depth.
Restrict window parameter usage.

* lisp/pdf-view.el (pdf-view-maybe-redisplay-resized-windows,
  pdf-view-new-window-function): Read and write window-parameter
  pdf-view-window-size in pdf-view-maybe-redisplay-resized-windows
  only.
Qualify info about updating.

* README.org: Restarting Emacs may be necessary.
Added new change page hook.

* lisp/pdf-view.el (pdf-view-change-page-hook): New hook ran after
  changing a page, but before redisplay.
  (pdf-view-goto-page): Run new hook.
Check for libpng availability.

* lisp/pdf-view.el (pdf-view-use-imagemagick): Extended documentation.
  (pdf-view-image-type): Check if png image-type is available.
  Fallback to imagemagick or signal an error. Extended documentation.
Check for libpng availability.

* lisp/pdf-view.el (pdf-view-use-imagemagick): Extended documentation.
  (pdf-view-image-type): Check if png image-type is available.
  Fallback to imagemagick or signal an error. Extended documentation.