Missing RestSharp dependency

[c-w]

Hi @pseudomuto,

First of all: thanks for creating this easy-to-use library.

One minor concern: the package available via NuGet seems to be missing a dependency on RestSharp. A basic use-case using ContentService, FileTarget and DiskFile leads to the following exception:

Adding a dependency on RestSharp fixes the problem. Sample packages.config file:

<?xml version="1.0" encoding="utf-8"?>
<packages>
  <package id="RestSharp" version="105.2.3" targetFramework="net452" />
</packages>

[pseudomuto]

Hey, thanks for looking into this! Any interest in making a PR?