refactor to a library, add integration tests

tests/parse.rs

@@ -0,0 +1,23 @@
+extern crate taskwarrior;
+extern crate chrono;
+
+use std::fs::File;
+use std::io::BufReader;
+use chrono::prelude::*;
+
+#[test]
+fn test_parse() {
+    let filename = "tests/data/tdb2-test.data";
+    let file = File::open(filename).unwrap();
+    let tasks = taskwarrior::parse(filename, BufReader::new(file)).unwrap();
+    assert_eq!(
+        tasks[0].description,
+        "https://phabricator.services.example.com/D7364 [taskgraph] Download debian packages"
+    );
+    assert_eq!(tasks[0].entry, Utc.timestamp(1538520624, 0));
+    assert_eq!(tasks[0].udas.get("phabricatorid").unwrap(), "D7364");
+    assert_eq!(tasks[1].annotations[0].entry, Utc.timestamp(1541461824, 0));
+    assert!(tasks[1].annotations[0].description.starts_with(
+        "https://github.com",
+    ));
+}