WIP: Try adding support for TimeSpan.ToString()

[MangelMaxime]

Hello @Jand42,

I was trying to add support for TimeSpan.ToString() but I am facing an issue.

When trying to build the Tests/Web project I am getting this error:

WEBSHARPERTASK : WebSharper error WS9001: Error running WIG assembly: System.Exception: No ExtensionAttribute set on the input assembly   at WebSharper.Compiler.CommandTools.LoadInterfaceGeneratorAssembly(Stri  
ng file, LoggerBase logger) in C:\Users\mmangel\Workspaces\Github\dotnet-websharper\core\feat-add-timespan-to-string\src\compiler\WebSharper.Compiler\CommandTools.fs:line 437   at WebSharper.Compiler.CommandTo  
ols.RunInterfaceGenerator(AssemblyResolver aR, FSharpOption`1 snk, WsConfig config, LoggerBase logger) in C:\Users\mmangel\Workspaces\Github\dotnet-websharper\core\feat-add-timespan-to-string\src\compiler\WebSh 
arper.Compiler\CommandTools.fs:line 440   at WebSharper.Compiler.FSharp.Compile.Compile@148-5.Invoke(Unit unitVar0) in C:\Users\mmangel\Workspaces\Github\dotnet-websharper\core\feat-add-timespan-to-string\src\  
compiler\WebSharper.Compiler.FSharp\Compile.fs:line 150 [C:\Users\mmangel\Workspaces\Github\dotnet-websharper\core\feat-add-timespan-to-string\src\stdlib\WebSharper.JavaScript\WebSharper.JavaScript.fsproj]      
    4 Warning(s)
    1 Error(s)

I took inspiration from how DateTime.ToString() was adding in f5f2784

Could you please hint me in the right direction?

I also want to add support for TimeSpan.TryParse.

[Jand42]

@MangelMaxime Sorry, I was busy on the backports and releases, I will take a look tomorrow!

[MangelMaxime]

@Jand42 No problem, thanks for all the work on the different issues (sorry for the spam of them) and back porting them to WS 6.