add statistics module

provides some basic statistics functions (sum, mean, etc.)
and a function to return the parameters of the linear regression of
two variables

implemented using num_traits to be more flexible for the types

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>

src/tools.rs

@@ -30,6 +30,7 @@ pub mod lru_cache;
 pub mod runtime;
 pub mod ticket;
 pub mod timer;
+pub mod statistics;
 pub mod systemd;
 
 mod wrapped_reader_stream;