Integration tests

Several tests for recursive dirs, hard & soft links.
Tests use the tempfile project.

Personally I find the tests hard to read. Am considering adding a
'--no-color' output option as this will make the tests much more
readable. (Currently we have to call format_string to get the matching
colors and if a test fails the diff is very hard to read).

Cargo.toml

@@ -7,3 +7,5 @@ authors = ["bootandy <bootandy@gmail.com>", "nebkor <code@ardent.nebcorp.com>"]
 ansi_term = "0.11"
 clap = "2.31"
 assert_cli = "0.5"
+tempfile = "3"
+