* Additions to documentations and type definitions
Added return types to documentation as well as modified return type definition to match actual types returned.
Used union types for promises where applicable.
Builds and gulp docs ok.
* Update file.ts
* Updates docs for CameraPreview, Base64ToGallery and Developer.MD
-DEVELOPER.md: Corrects 'npm run tslint' instruction to 'npm run lint'
-CameraPreview: Fixes syntax error in hide
-Base64ToGallery: Adds desc of options obj props
* Fixes resolveLocalFileSystemURL bug in File.readAsText() and adds File.readAsDataUrl()
- File.readAsText(): window.resolveLocalFileSystemURL() was incorrectly implemented
* Updates callback arg in File.checkFile()
Callback arg of window.resolveLocalFileSystemURL was fileSystem, but it actually returns fileEntry
* Corrects repo link and comments out setFlashMode()
- Repo prop and link in desc were not pointing to the same gh repo as the plugin
- setFlashMode() is not currently available in the repo that gets pulled by the corodova plugin
In some cases the incoming ```path``` variable may not necessarily contain a trailing slash, but in cases where the directory path is manually built within the plugin this was not protected against. This shouldn't be a big issue if consumers are using ```cordova.file.*``` for the path params, but not all consumers may be using this.
