Twoflower?

• do not convert metric names to lists
• gauge:set_to_current_timestamp/1,2,3
• disallow 'quantile' label for summary
• test histogram label 'le' is invalid
• gauge:track_inprogress/2,3,4
• summary:observe_duration/2,3,4
• histogram:observe_duration/2,3,4
• deprecate histogram bounds option, introduce histogram buckets option and default buckets.
• linear histogram buckets generator
• exponential histogram buckets generator