Glimpse v2 - API for submitting messages to timeline

Currently, if I want to register an event, I have to somehow get an instance of the messages bus, create a custom class create own stopwatch or get a hold of the registered `Func<IExecutionTimer>` and then profile the desired code. All of this take a lot more lines of code than it should.

This should be a one liner for moment in time events or a simple using statement if its a duration event. Any solution probably should be able to be accessed statically and a null provider registered in this hook so that the code works for testing, but when my code fully runs, it uses a real provider.

As per @nikmd23:
> I've refactored the code and updated the class names. Now you can use these two entry points like so:

1. As a user, modify configuration:

    ```c#
    GlimpseConfiguration.Override = config => 
    {
        // modify the configuration
    };
    ````
2. As a user, capture a timing event:

    ```c#
    using(GlimpseTimeline.Capture("Some chunk of code to measure"))
    {
        // some custom user code
    }
    ```
3. As a user, capture a moment in time for the timeline:

    ```c#
    GlimpseTimeline.CaptureMoment("Some event I want to mark in the timeline");
    ```