use style property for sizing hotspots content rather than width
Allow adding additional css files to the embedded html

Useful for using, (for example) fontawesome icons for hotspots
Added zoom support to CSS 3D renderer.
Actually use hfov instead of vfov.
Updated default field of view.
Fixed bug with tours.
Fix bug with hotspots not appearing.
Fix bug with CSS 3D dragging.
Fix bug in last commit.
Add fallback tiles to multires generation script.
Transition changelog to Markdown.
Added ability to add content to header (e.g. custom CSS).
Fixed duplicated hotspots bug.
Add 1px border to remove thin lines visible in CSS renderer.
Fix tour bug.
Merge branch 'master' of https://github.com/mpetroff/pannellum.git into hotspots
Remove code that was superseeded by mpetroffs' c792b36d

Meaning that the css keyword in json is replaced by a header keyword
taking an html string as value. Example file updated accordingly