Null instead of empty object for pdf
Assume pages have the same height 

- This not true sometimes, but often enough to be reasonable.
Properly calculate document offset
Update pdf.js
Style tweaks
[WIP] Start working on dispatcher
Minor fixes to documentation
Update PDF.js
Add link to Storm
Merge branch 'develop'

* develop:
  Add link to Storm
  Update PDF.js
  Minor fixes to documentation
  [WIP] Start working on dispatcher
  Style tweaks
  Update pdf.js
  Properly calculate document offset
  Assume pages have the same height
  Null instead of empty object for pdf