ustr: new package

[Thomas:
 - Fix typo in patch description.
 - Remove trailing whitespace in Config.in.
 - Fix Config.in comment to match what's specified in the Buildroot
   manual.
 - Adjust .mk logic to use BR2_STATIC_LIBS vs. BR2_SHARED_LIBS instead
   of BR2_PREFER_STATIC_LIB, and therefore support the installation of
   only the shared library.
 - Remove the libustr-debug library from the target and staging
   directories, it's the same as libustr, except that it's compiled
   with debugging symbols.
 - Always install only the shared variant of the library for
   host-ustr.]

Signed-off-by: Clayton Shotwell <clshotwe@rockwellcollins.com>
Signed-off-by: Matt Weber <matthew.weber@rockwellcollins.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
diff --git a/package/Config.in b/package/Config.in
index 850fc09..307c473 100644
--- a/package/Config.in
+++ b/package/Config.in
@@ -968,6 +968,7 @@
 	source "package/readline/Config.in"
 	source "package/slang/Config.in"
 	source "package/tclap/Config.in"
+	source "package/ustr/Config.in"
 endmenu
 
 endmenu