refactor fixedbuffer, add mjson

[matrix_esp_thesis] / ext / mjson

diff --git a/ext/mjson b/ext/mjson
new file mode 160000 (submodule)
index 0000000..b766f34
--- /dev/null
+++ b/ext/mjson
@@ -0,0 +1 @@
+Subproject commit b766f343bf68b8ea89889055acbf8aef820e2b71