Fixed #369 - The parameter passing was wrong due to a typo. The
deserialization of the 'package.json' will now work as expected.
- DRY-ed the internal structure a little bit.
- Implemented a function which converts the HTTP response headers
  (string) to an object.
Removed the lower case transformation.
Extended the API so that it is possible to open the preview pane from within a package (#362).
Merge pull request #380 from akoenig/http-data-type-fix

Fixed `dataType` in HTTP GET API.
Merge pull request #381 from akoenig/http-header-conversion

Conversion of the HTTP response headers
Merge pull request #383 from akoenig/api-open-preview

API: Open a preview pane from within a package.
Move manual to separate repo
Added manual as submodule
Merge remote-tracking branch 'upstream/master'