zstring: Add class

This is the most efficient wrapper for nul-terminated strings as it does
not care about determining string length. Conversions to / from
ztring_view are provided to make it trivial to upgrade.

Change-Id: Ic83626c53b95b851c3c4a13b1eded8f1e40539f0
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/src/meson.build b/src/meson.build
index a59cffd..204110f 100644
--- a/src/meson.build
+++ b/src/meson.build
@@ -44,6 +44,7 @@
 stdplus_srcs = [
   'exception.cpp',
   'signal.cpp',
+  'zstring.cpp',
   'zstring_view.cpp',
 ]