Support csc.exe path configuration via standard provider options in web.config/app.config

[cmlr72]

The roslyn compiler path should be configurable via documented configuration settings instead of internal implementation details like environment variables.
The providerOption element under system.codedom/compilers/compiler is officially documented and also used by the integrated CodeDomProvider, e.g.

<system.codedom>
   <compilers>
    <compiler language="c#;cs;csharp" extension=".cs" warningLevel="4" type="Microsoft.CSharp.CSharpCodeProvider, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089">
      <providerOption name="CompilerVersion" value="v4.0"/>
      <providerOption name="WarnAsError" value="false"/>
     </compiler>
   </compilers>
</system.codedom>

So the RoslynCodeDomProvider should support something like

<compiler language="c#;cs;csharp" extension=".cs" type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.CSharpCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform" warningLevel="4" compilerOptions="/langversion:default /nowarn:1659;1699;1701">
   <providerOption name="CompilerPath" value="..\my\path\to\csc.exe"/>
</compiler>

[cmlr72]

Same for TTL-Option

[twsouthwick]

I believe this is solved by #55 and #63

[StephenMolloy]

support was added in 3.5 with #102.