Add IncludeXmlComments overload that accepts assembly

[leotsarev]

Hey!

Thank you for this awesome project.
Frequently I need to include Xml comments into Swagger, so I have to call IncludeXmlComments and pass here name of Xml file. It's inconvenient to hard code file name, and I have to construct it from assembly name.
I propose to include following convenience helper/overload:

public static void IncludeXmlCommentsForAssembly(
  this SwaggerGenOptions swaggerGenOptions,
  Assembly assembly,
  bool includeControllerXmlComments = false)  => 

    swaggerGenOptions.IncludeXmlComments(
      Path.Combine(AppContext.BaseDirectory, $"{assembly.GetName().Name}.xml"), 
      includeControllerXmlComments);

If you like it, I'll submit a PR

[Havunen]

Sounds good to me, you can open PR to https://github.com/Havunen/DotSwashbuckle