Implement outlier detection using LOF

Outlier detection is an unsupervised algorithm for detecting outliers
in groups of points (in the abstract sense) by computing local reachability density based on a specified number of neighbours.

Author: urschrei

geo/CHANGES.md

@@ -2,7 +2,8 @@
 
 ## Unreleased
 
-*
+* Added outlier detection algorithm using [LOF](https://en.wikipedia.org/wiki/Local_outlier_factor)
+  * <https://github.com/georust/geo/pull/904>
 
 ## 0.23.0
 

geo/src/algorithm/mod.rs

@@ -218,3 +218,7 @@ pub use within::Within;
 
 /// Planar sweep algorithm and related utils
 pub mod sweep;
+
+/// Detect outliers in a group of points using [LOF](https://en.wikipedia.org/wiki/Local_outlier_factor)
+pub mod outlier_detection;
+pub use outlier_detection::OutlierDetection;