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.

src/tc/Task.cpp

@@ -0,0 +1,115 @@
+////////////////////////////////////////////////////////////////////////////////
+//
+// Copyright 2022, Dustin J. Mitchell
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included
+// in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+// THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+//
+// https://www.opensource.org/licenses/mit-license.php
+//
+////////////////////////////////////////////////////////////////////////////////
+
+#include <cmake.h>
+#include <assert.h>
+#include "tc/Task.h"
+#include "tc/util.h"
+
+using namespace tc::ffi;
+
+////////////////////////////////////////////////////////////////////////////////
+tc::Task::Task (TCTask *tctask)
+{
+  inner = unique_tctask_ptr(
+      tctask,
+      [](TCTask* task) { tc_task_free(task); });
+}
+
+////////////////////////////////////////////////////////////////////////////////
+tc::Task::Task (Task &&other) noexcept
+{
+  // move inner from other
+  inner = unique_tctask_ptr(
+      other.inner.release(),
+      [](TCTask* task) { tc_task_free(task); });
+}
+
+////////////////////////////////////////////////////////////////////////////////
+tc::Task& tc::Task::operator= (Task &&other) noexcept
+{
+  if (this != &other) {
+    // move inner from other
+    inner = unique_tctask_ptr(
+        other.inner.release(),
+        [](TCTask* task) { tc_task_free(task); });
+  }
+  return *this;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+std::string tc::Task::get_uuid () const
+{
+  auto uuid = tc_task_get_uuid(&*inner);
+  return tc2uuid(uuid);
+}
+
+////////////////////////////////////////////////////////////////////////////////
+tc::Status tc::Task::get_status () const
+{
+  auto status = tc_task_get_status(&*inner);
+  return tc::Status(status);
+}
+
+////////////////////////////////////////////////////////////////////////////////
+std::map <std::string, std::string> tc::Task::get_taskmap () const
+{
+  TCKVList kv = tc_task_get_taskmap (&*inner);
+  if (!kv.items) {
+    throw task_error ();
+  }
+
+  std::map<std::string, std::string> taskmap;
+  for (size_t i = 0; i < kv.len; i++) {
+    auto k = tc2string_clone(kv.items[i].key);
+    auto v = tc2string_clone(kv.items[i].value);
+    taskmap[k] = v;
+  }
+
+  return taskmap;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+std::string tc::Task::get_description () const
+{
+  auto desc = tc_task_get_description(&*inner);
+  return tc2string(desc);
+}
+
+////////////////////////////////////////////////////////////////////////////////
+std::string tc::Task::task_error () const {
+  TCString error = tc_task_error (&*inner);
+  std::string errmsg;
+  if (!error.ptr) {
+    errmsg = std::string ("Unknown TaskChampion error");
+  } else {
+    errmsg = std::string (tc_string_content (&error));
+  }
+  tc_string_free (&error);
+  return errmsg;
+}
+
+////////////////////////////////////////////////////////////////////////////////