Implement basic installation of file to directory

Bare minimum functionality of `install file dir` implemented.
Also added TODO markers in code for outstanding parameters
and split main function into smaller logical chunks.

tests/test_install.rs

@@ -19,3 +19,20 @@ fn test_install_help() {
 
 //    assert!(result.stdout.contains("Usage:"));
 }
+
+#[test]
+fn test_install_basic() {
+    let (at, mut ucmd) = testing(UTIL_NAME);
+    let dir = "test_install_target_dir_dir";
+    let file = "test_install_target_dir_file_a";
+
+    at.touch(file);
+    at.mkdir(dir);
+    let result = ucmd.arg(file).arg(dir).run();
+
+    assert_empty_stderr!(result);
+    assert!(result.success);
+
+    assert!(!at.file_exists(file));
+    assert!(at.file_exists(&format!("{}/{}", dir, file)));
+}