docs: update openmetrics links to v1.0.0 release (#253)

Signed-off-by: David Ashpole <[email protected]>

Author: dashpole

Diff for: src/encoding/protobuf.rs

@@ -14,7 +14,7 @@
 //! #   counter.clone(),
 //! # );
 //! # counter.inc();
-//! // Returns `MetricSet`, the top-level container type. Please refer to [openmetrics_data_model.proto](https://github.com/OpenObservability/OpenMetrics/blob/main/proto/openmetrics_data_model.proto) for details.
+//! // Returns `MetricSet`, the top-level container type. Please refer to [openmetrics_data_model.proto](https://github.com/prometheus/OpenMetrics/blob/v1.0.0/proto/openmetrics_data_model.proto) for details.
 //! let metric_set = encode(&registry).unwrap();
 //!
 //! let family = metric_set.metric_families.first().unwrap();

Diff for: src/encoding/text.rs

@@ -53,7 +53,7 @@ use std::fmt::Write;
 ///
 /// Use [`encode_registry`] or [`encode_eof`] if partial encoding is needed.
 ///
-/// See [OpenMetrics exposition format](https://github.com/OpenObservability/OpenMetrics/blob/main/specification/OpenMetrics.md#text-format)
+/// See [OpenMetrics exposition format](https://github.com/prometheus/OpenMetrics/blob/v1.0.0/specification/OpenMetrics.md#text-format)
 /// for additional details.
 ///
 /// # Examples