Min, Max, Percentile Metric Aggregations

[eqinox76]

Is your feature request related to a problem? Please describe.
I see several use cases for Min, Max, Percentile aggregations on client side. But i see no way to export them via the opencensus api.
One example would be fill percentage of a internal buffer. Normally you are interested in the max, average and min fill percentage. With opencensus atm you could only export LastValue (with e.g. stackdriver this would be sampled once per minute and nearly useless) or the average by using Sum and Count.

Describe the solution you'd like
A new Aggregation which supports Percentiles (where Min and Max are special cases). E.g.

Aggregation: view.Percentiles(0., 0.50, 0.95, 1.0),

To get the minimum, mean, 95th percentile and maximum values during the last reporting period.

Describe alternatives you've considered
My understanding may be incomplete and i have not found a good explanation yet.

Additional context
Related tickets:
opencensus-specs
opencensus-java