Added meson build support

bench/meson.build

@@ -0,0 +1,13 @@
+benchmark = dependency('benchmark')
+
+bench_matrix = [
+  ['bench',           [spdlog_dep],            []],
+  ['async_bench',     [spdlog_dep],            []],
+  ['formatter-bench', [spdlog_dep, benchmark], ['all']],
+  ['latency',         [spdlog_dep, benchmark], []],
+]
+
+foreach i : bench_matrix
+  bench_exe = executable(i[0], i[0] + '.cpp', dependencies: i[1])
+  benchmark('bench_' + i[0], bench_exe, args: i[2])
+endforeach