Misleading documentation due to markdown processing

[GREsau]

The doc comment for total_scheduled_count contains this:

    /// ##### Definition
    /// This metric is equal to [`total_short_delay_duration`][TaskMetrics::total_short_delay_duration]
    /// + [`total_long_delay_duration`][TaskMetrics::total_long_delay_duration].

...which looks fine, until it's rendered as markdown (https://docs.rs/tokio-metrics/0.3.1/tokio_metrics/struct.TaskMetrics.html#definition):

As you can see, the line beginning with a + is interpreted as a bullet point. The way this is displayed implies that total_scheduled_count is equal to total_short_delay_duration, which left me very confused!

This also affects total_scheduled_duration, total_poll_count and total_poll_duration