Added goal - "Make installable apps sharable"
Removed API (closes #157)

* removed API mention in Abstract
* removed examples
* removed other mentions of requestBookmark()
Merge pull request #159 from w3c/remove_api

Removed API (closes #157)
Removed API from V1
cleaned up markup
Added extension point to manifest processing algo (closes #156)
fixed typo: not supported -> unsupported /g
Merge pull request #160 from w3c/extension-point

Added extension point to manifest processing algo (closes #156)
Merge branch 'gh-pages' of github.com:w3c/manifest into gh-pages
removed `unknown` display mode (closes #163)
Merge pull request #165 from w3c/remove_unknow

removed `unknown` display mode (closes #163)