Add a tagged method, and some additional functionality around the request fields and tags.

[anoldguy]

Block Usage:

Rackstash.tagged(:foo) { Rails.logger.info "Hello" }

Set-and-forget Usage:

Rackstash.tagged(:foo)
Rails.logger.info "Hello"

Also, bring similar functionality to the request fields:

  config.rackstash.request_tags = [
    lambda { |request| request.subdomains.first || "no-account" },
    lambda { |request|
      case
      when request.subdomains.first == "monitoring"
        "monitoring"
      when request.path.starts_with?("/foo")
        "foo"
      else
        "web"
      end
    }
  ]