Prometheus-flask-instrumentator

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Added

* The observed latency values can now be rounded to a certain number of
decimals as an opt-in feature. This can improve bytes per sample required in
storage solutions like VictoriaMetrics.
* Updates to the documentation.

Added

* Method `expose()` implements a way to expose the metrics by adding an
endpoint to a given Flask app. Compatible with multiprocess mode.
* Add import alternative `Instrumentator`.

Changed

* Rename class to `PrometheusFlaskInstrumentator` from `FlaskInstrumentator`.
* Switch to SemVer versioning.
* Split instrumentation and exposition into two parts.
* Moved pass of Flask object from constructor to `instrument()` method.
* Extended testing.