Create a builder implementation for use with ConfigureServices

[mikegoatly]

Ideally I'd like to be able to fully configure an implementation of IFullTextIndex such that it's injectable in a fully configured state.

[mikegoatly]

This should be a separate nuget package Lifti.Extensions.Microsoft.DependencyInjection?

[mikegoatly]

Closing this because it's not hard as it stands to do something like this:

services.AddSingleton<IFullTextIndex<int>>(
    new FullTextIndexBuilder<int>()
         // Your config here
         .Build());