adopt actix-limitation crate (#229)

* import code from actix-limitation master branch

* fix compilation

* update legal info

* fix compile errors

* ignore failing tests

* remove futures dep

* add changelog

* update readme

* fix doc test example

actix-limitation/src/core/status/mod.rs

@@ -0,0 +1,58 @@
+use crate::Error as LimitationError;
+use chrono::SubsecRound;
+use std::{convert::TryInto, ops::Add, time::Duration};
+
+/// A report for a given key containing the limit status.
+///
+/// The status contains the following information:
+///
+/// - [`limit`]: the maximum number of requests allowed in the current period
+/// - [`remaining`]: how many requests are left in the current period
+/// - [`reset_epoch_utc`]: a UNIX timestamp in UTC approximately when the next period will begin
+#[derive(Clone, Debug)]
+pub struct Status {
+    pub(crate) limit: usize,
+    pub(crate) remaining: usize,
+    pub(crate) reset_epoch_utc: usize,
+}
+
+impl Status {
+    pub fn limit(&self) -> usize {
+        self.limit
+    }
+
+    pub fn remaining(&self) -> usize {
+        self.remaining
+    }
+
+    pub fn reset_epoch_utc(&self) -> usize {
+        self.reset_epoch_utc
+    }
+
+    pub(crate) fn build_status(count: usize, limit: usize, reset_epoch_utc: usize) -> Self {
+        let remaining = if count >= limit { 0 } else { limit - count };
+
+        Status {
+            limit,
+            remaining,
+            reset_epoch_utc,
+        }
+    }
+
+    pub(crate) fn epoch_utc_plus(duration: Duration) -> Result<usize, LimitationError> {
+        match chrono::Duration::from_std(duration) {
+            Ok(value) => Ok(chrono::Utc::now()
+                .add(value)
+                .round_subsecs(0)
+                .timestamp()
+                .try_into()
+                .unwrap_or(0)),
+            Err(_) => Err(LimitationError::Other(
+                "Source duration value is out of range for the target type".to_string(),
+            )),
+        }
+    }
+}
+
+#[cfg(test)]
+mod test;