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/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)