reorganize process related sources into a process/ directory

src/lib.rs

@@ -1,7 +1,5 @@
 mod error;
-mod handle;
 mod process;
-mod snapshot;
 
 pub use error::Error;
 pub use process::{Identifier, Process};

src/process/mod.rs

@@ -0,0 +1,5 @@
+mod handle;
+mod process;
+mod snapshot;
+
+pub use process::{Identifier, Process};

src/process/process.rs

@@ -1,4 +1,4 @@
-use crate::{handle::Handle, snapshot};
+use super::{handle::Handle, snapshot};
 
 use derive_more::derive::Display;