Refactor with the help of Clippy (#462)

We add clippy as our build — also rectifying the missing `plume-cli` build!

In the next step we follow clippy's advise and fix some of the "simple" mistakes in our code, such as style or map usage.

Finally, we refactor some hard bits that need extraction of new types, or refactoring of function call-types, especially those that thread thru macros, and, of course functions with ~15 parameters should probably be rethought.

plume-cli/src/search.rs

@@ -60,13 +60,7 @@ fn init<'a>(args: &ArgMatches<'a>, conn: &Connection) {
     let path = Path::new(path).join("search_index");
 
     let can_do = match read_dir(path.clone()) { // try to read the directory specified
-        Ok(mut contents) => {
-            if contents.next().is_none()  {
-                true
-            } else {
-                false
-            }
-        },
+        Ok(mut contents) =>  contents.next().is_none(),
         Err(e) => if e.kind() == ErrorKind::NotFound {
             true
         } else {
@@ -107,5 +101,3 @@ fn unlock<'a>(args: &ArgMatches<'a>) {
 
     remove_file(path).unwrap();
 }
-
-