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/util.cpp

@@ -0,0 +1,81 @@
+////////////////////////////////////////////////////////////////////////////////
+//
+// 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 <format.h>
+#include <assert.h>
+#include "tc/Replica.h"
+#include "tc/Task.h"
+
+using namespace tc::ffi;
+
+namespace tc {
+////////////////////////////////////////////////////////////////////////////////
+TCString string2tc (const std::string& str)
+{
+  return tc_string_clone_with_len (str.data (), str.size ());
+}
+
+////////////////////////////////////////////////////////////////////////////////
+std::string tc2string_clone (const TCString& str)
+{
+  size_t len;
+  auto ptr = tc_string_content_with_len (&str, &len);
+  auto rv = std::string (ptr, len);
+  return rv;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+std::string tc2string (TCString& str)
+{
+  auto rv = tc2string_clone(str);
+  tc_string_free (&str);
+  return rv;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+TCUuid uuid2tc(const std::string& str)
+{
+  TCString tcstr = tc_string_borrow(str.c_str());
+  TCUuid rv;
+  if (TC_RESULT_OK != tc_uuid_from_str(tcstr, &rv)) {
+    throw std::string ("invalid UUID");
+  }
+  return rv;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+std::string tc2uuid (TCUuid& uuid)
+{
+  char s[TC_UUID_STRING_BYTES];
+  tc_uuid_to_buf (uuid, s);
+  std::string str;
+  str.assign (s, TC_UUID_STRING_BYTES);
+  return str;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+}