Implemented regexp searching.

* src/epdfinfo.h (NORMALIZE_PAGE_ARG): New macro for page arg normalization.

* src/epdfinfo.c:
(region_print): New function printing a cairo_region_t response.
(cmd_search_string): Use above macro/function.
(cmd_search_regexp): New function searching for regexps in a document.

* lisp/pdf-info.el (pdf-info-search): Documentation fix.
  (pdf-info-re-search) New interface function for regexp search.
Cleaned up whitespace.
Cleanup.
Make treat-newline-p default.

* lisp/pdf-info.el (pdf-info-re-search): Make treat-newline-p default.
Renamed function.

* lisp/pdf-info.el (pdf-info-search-string, pdf-info-search-regexp,
  pdf-info-pagelinks): Renamed pdf-info-search and pdf-info-re-search.

* lisp/pdf-occur.el (pdf-occur): Use new names.

* lisp/pdf-isearch.el (pdf-isearch-search-page,
  pdf-isearch-find-next-matching-page): Use new names.
Removed function alias.

* lisp/pdf-view.el (pdf-util-image-size): Deleted.

* lisp/pdf-sync.el (pdf-sync-correlate-tex, pdf-sync-display-pdf): Use
  pdf-view-image-size.
Documentation fix.

* lisp/pdf-view.el (pdf-view-dark-minor-mode): Documentation fix.
Handle regexp responses.

* lisp/pdf-info.el (pdf-info-query--transform-response): Use new command names.
  (pdf-info-search-regexp): Fixed typo.
Added TODO items.