Consolidate nuspec into csproj (#135)

Most information from nuspec can be specified in the csproj.
This has the benefit that all information is located in a single place and that previously duplicated information can no longer be out of sync.
Currently release notes and package dependencies are out of sync.

I've added the following:
* Xavier Fischer as Author.
* Referred MIT license directly instead of throught `LICENSE.MD`
* link to github project page
* link to git repository

csproj does not support the concepts of `<owners>` and `<language>` so I've left them out.

The following tags are automatically inferred:
* `<id>` from project name
* `requireLicenseAcceptance` defaults to `false`
* `AssemblyVersion` is `$(Version).0`

Some good resources:
* https://github.com/NuGet/Home/wiki/Adding-nuget-pack-as-a-msbuild-target
* https://andrewlock.net/version-vs-versionsuffix-vs-packageversion-what-do-they-all-mean/

Author: jnyrup

GeoJSON.Net.nuspec

@@ -2,20 +2,22 @@
 
   <PropertyGroup>
     <TargetFrameworks>netstandard1.0;netstandard1.1;net35;net40;net45;</TargetFrameworks>
-    <AssemblyName>GeoJSON.Net</AssemblyName>
-    <AssemblyVersion>1.1.73</AssemblyVersion>
-    <FileVersion>1.1.73</FileVersion>
     <Description>.Net types for the GeoJSON RFC to be used with Json.Net</Description>
-    <Authors></Authors>
+    <Authors>Matt Hunt;Joerg Battermann;Xavier Fischer</Authors>
     <Company>GeoJSON.Net</Company>
     <Copyright>Copyright © Joerg Battermann, Matt Hunt, Xavier Fischer and Contributors, 2014 - 2019</Copyright>
     <GeneratePackageOnBuild>true</GeneratePackageOnBuild>
     <Version>1.1.73</Version>
+    <PackageProjectUrl>https://github.com/GeoJSON-Net/GeoJSON.Net</PackageProjectUrl>
+    <RepositoryUrl>https://github.com/GeoJSON-Net/GeoJSON.Net.git</RepositoryUrl>
+    <RepositoryType>git</RepositoryType>
+    <PackageTags>geojson;geo;json;geolocation</PackageTags>
+    <PackageLicenseExpression>MIT</PackageLicenseExpression>
     <PackageReleaseNotes>Assembly is now strong named</PackageReleaseNotes>
   </PropertyGroup>
 
   <ItemGroup>
     <PackageReference Include="Newtonsoft.Json" Version="10.0.2" />
   </ItemGroup>
-  
+
 </Project>