Update NEWS for 0.5.1

NEWS

+Changes for 0.5.1 'Asiatic Cheetah':
+------------------------------------
+
+0.5.1 is a small release improving speeds and fixing minor issues
+compared to 0.5.0:
+ - SSE2 optimizations for CDEF, wiener and warp_affine
+ - NEON optimizations for SGR on ARM32
+ - Fix mismatch issue in x86 asm in inverse identity transforms
+ - Fix build issue in ARM64 assembly if debug info was enabled
+
+
 Changes for 0.5.0 'Asiatic Cheetah':
-----------------------------
+------------------------------------
 
 0.5.0 is a medium release fixing regressions and minor issues,
 and improving speed significantly:

meson.build

@@ -23,7 +23,7 @@
 # SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 project('dav1d', ['c'],
-    version: '0.5.0',
+    version: '0.5.1',
     default_options: ['c_std=c99',
                       'warning_level=2',
                       'buildtype=release',