Code optimization; new functions

[kaushalmodi]

• Use of funcall to call the right command based on if the user uses pdf-tools package or not
• Refine interleave--doc-view-kill-proc-and-buffer fn so that the doc-view-kill-proc is called only if the major mode is doc-view-mode.
• Added *interleave--pdf-buffer*; renamed interleave--org-buf to interleave--org-buffer
• Use of switch-to-buffer and switch-to-buffer-other-window instead of (other-window 1) for more accuracy (in the event the user has opened a buffer other than the pdf or org notes file in the "other" window).
• Added commands to synchronize the pdf page with the page displayed in current org notes buffer, to sync the pdf page to the next/previous notes page:
  • interleave--sync-pdf-page-current
  • interleave--sync-pdf-page-previous
  • interleave--sync-pdf-page-next
• Creates variable handles interleave-map and interleave-pdf-mode-map so a user can customize the key bindings in them without having to modify the source.
• Changed the lighter strings for both pdf and org buffer minor modes to " ≡"

[kaushalmodi]

I need to understand why I see this note on the pull request page: "Can't automatically merge. Don't worry, you can still create the pull request."

[kaushalmodi]

Changed the search to org heading properties instead of "Notes for page" string in https://github.com/kaushalmodi/interleave/commit/3fff9d9001989a5ae9bf2666bf6c32ceef930ff3

Improved robustness in https://github.com/kaushalmodi/interleave/commit/e5a8304c8a33d79f56d6ac7afbbbbafb57db828b

[rudolfochrist]

Works like a charm. Especially the buffer synchronization is a nice enhancement. Thank you.