str/conv: Add basic functions

We need some basic templates for formatting into a buffer or fmtlib to
make other conversions straightforward.

Change-Id: I8c13175394f6b4fd4a55edf8d653e98a1562cc64
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/test/meson.build b/test/meson.build
index a92e411..1239296 100644
--- a/test/meson.build
+++ b/test/meson.build
@@ -16,6 +16,7 @@
   'str/buf': [stdplus_dep, gtest_main_dep],
   'str/cat': [stdplus_dep, gtest_main_dep],
   'str/cexpr': [stdplus_dep, gtest_main_dep],
+  'str/conv': [stdplus_dep, gmock_dep, gtest_main_dep],
   'str/maps': [stdplus_dep, gmock_dep, gtest_main_dep],
   'util/cexec': [stdplus_dep, gtest_main_dep],
   'variant': [stdplus_dep, gtest_main_dep],