Add a C++ wrapper around TC FFI

This uses CMake to build a simple Rust library (in `src/tc/rust`) that
just re-exports everything from the `taskchampion-lib` crate.

The C++ wrappers then wrap this into C++ objects with proper lifecycle
maintenance, in the `tc` namespace.

The C++ wrappers are incomplete, and missing methods are tagged with
"TODO".  These will be added as needed.

docs/contrib/branching.md

@@ -11,7 +11,7 @@ Taskwarrior and Taskserver use the same branching model.
 ## Git Branching
 
 Git allows arbitrary and low-cost branching, which means that any branching model can be used.
-A new Git repository has one branch, the default branch, named `master`, but even this is not required.
+A new Git repository has one branch, the default branch, named `stable`, but even this is not required.
 
 [![master](master.png)](master.png)
 

docs/contrib/rust-and-c++.md

@@ -0,0 +1,29 @@
+# Rust and C++
+
+Taskwarrior has historically been a C++ project, but as part of an [ongoing effort to replace its storage backend](https://github.com/GothenburgBitFactory/taskwarrior/issues/2770) it now includes a Rust library called TaskChampion.
+To develop Taskwarrior, you will need both a [C++ compiler and tools](./development.md), and a [Rust toolchain](https://www.rust-lang.org/tools/install).
+However, most tasks will only require you to be familiar with one of the two languages.
+
+## TaskChampion
+
+TaskChampion implements storage and access to "replicas" containing a user's tasks.
+It defines an abstract model for this data, and also provides a simple Rust API for manipulating replicas.
+It also defines a method of synchronizing replicas and provides an implementation of that method in the form of a sync server.
+TaskChampion provides a C interface via the `taskchampion-lib` crate.
+
+Other applications, besides Taskwarrior, can use TaskChampion to manage tasks.
+Applications written in Rust can use the `taskchampion` crate, while those in other languages may use the `taskchampion-lib` crate.
+Taskwarrior is just one application using the TaskChampion interface.
+
+You can build Taskchampion locally by simply running `cargo build` in the root of this repository.
+The implementation, including more documentation, is in the [`rust`](../../rust) subdirectory.
+
+## Taskwarrior's use of TaskChampion
+
+Taskwarrior's interface to TaskChampion has a few laters:
+
+* The skeletal Rust crate in [`src/tc/rust`](../../src/tc/rust) brings the symbols from `taskchampion-lib` under CMake's management.
+  The corresponding header file is included from [`rust/lib`](../../rust/lib).
+  All of these symbols are placed in the C++ namespace, `tc::ffi`.
+* C++ wrappers for the types from `taskchampion-lib` are defined in [`src/tc`](../../src/tc), ensuring memory safety (with `unique_ptr`) and adding methods corresponding to the Rust API's methods.
+  The wrapper types are in the C++ namespace, `tc`.

docs/index.md

@@ -7,12 +7,13 @@ For all other documenation, see https://taskwarrior.org.
 
 ## Contributing to Taskwarrior
 
- * [How to become an Open Source Contributor](./contrib/first_time)
- * [Contributing to Taskwarrior](./contrib/contribute)
- * [Developing Taskwarrior](./contrib/development)
- * [Building Taskwarrior](./contrib/build)
- * [Coding Style](./contrib/coding_style)
- * [Branching Model](./contrib/branching)
+ * [How to become an Open Source Contributor](./contrib/first_time.md)
+ * [Contributing to Taskwarrior](./contrib/contribute.md)
+ * [Developing Taskwarrior](./contrib/development.md)
+ * [Building Taskwarrior](./contrib/build.md)
+ * [Coding Style](./contrib/coding_style.md)
+ * [Branching Model](./contrib/branching.md)
+ * [Rust and C++](./contrib/rust-and-c++.md)
 
 ## RFC's
 
@@ -21,14 +22,14 @@ This is where design documents (RFCs) are kept.
 Although these documents are less formal than [IETF RFCs](https://www.ietf.org/rfc) they serve a similar purpose.
 These documents apply only to the Taskwarrior family of products, and are placed here to invite comment before designs finalize.
 
- -   [General Plans](./rfcs/plans)
- -   [Rules System](./rfcs/rules)
- -   [Full DOM Support ](./rfcs/dom)
- -   [Work Week Support](./rfcs/workweek)
- -   [Recurrence](./rfcs/recurrence)
- -   [Taskwarrior JSON Format](./rfcs/task)
- -   [CLI Updates ](./rfcs/cli)
- -   [Taskserver Sync Protocol](./rfcs/protocol)
- -   [Taskserver Message Format](./rfcs/request)
- -   [Taskserver Sync Algorithm](./rfcs/sync)
- -   [Taskserver Client](./rfcs/client)
+ -   [General Plans](./rfcs/plans.md)
+ -   [Rules System](./rfcs/rules.md)
+ -   [Full DOM Support ](./rfcs/dom.md)
+ -   [Work Week Support](./rfcs/workweek.md)
+ -   [Recurrence](./rfcs/recurrence.md)
+ -   [Taskwarrior JSON Format](./rfcs/task.md)
+ -   [CLI Updates ](./rfcs/cli.md)
+ -   [Taskserver Sync Protocol](./rfcs/protocol.md)
+ -   [Taskserver Message Format](./rfcs/request.md)
+ -   [Taskserver Sync Algorithm](./rfcs/sync.md)
+ -   [Taskserver Client](./rfcs/client.md)