Update PCLExt.FileStorage.nuspec

Latest changes sync (#30)

Returned UWP
Using appveyor only

Update .travis.yml

Small fixes

Added inheritdoc to ToString
Fixed UWP nuget
contents typo

Added TempRootFolder and DocumentsFolder

Added UWP and Test project
Replaced Storage word with Root in folders
ToString() returns the full path now
Fixed iOS test
Did something with Android project

Preparations for release

Updated version, corrected nuspec, fixes

Added .NET Standard support

Removed IFileSystem and everything related to it, using different concept of already established classes for specific files/folder

Added .NET Standard support

Removed IFileSystem and everything related to it, using different concept of already established classes for specific files/folder

Fixed GetFiles

Added new methods in FileExtensions