Switch to a command-line API closer to TaskWarrior

* Use a parser (rather than clap) to process the command line
* Outline some generic support for filtering, reporting, modifying, etc.
* Break argument parsing strictly from invocation, to allow independent testing

taskchampion/src/task.rs

@@ -42,7 +42,7 @@ impl Priority {
 }
 
 /// The status of a task.  The default status in "Pending".
-#[derive(Debug, PartialEq)]
+#[derive(Debug, PartialEq, Clone)]
 pub enum Status {
     Pending,
     Completed,

taskchampion/src/taskstorage/mod.rs

@@ -2,13 +2,11 @@ use failure::Fallible;
 use std::collections::HashMap;
 use uuid::Uuid;
 
-#[cfg(test)]
 mod inmemory;
 mod kv;
 mod operation;
 
 pub use self::kv::KVStorage;
-#[cfg(test)]
 pub use inmemory::InMemoryStorage;
 
 pub use operation::Operation;