remove unmaintained json crate, do our own string escaping

Cargo.lock

@@ -1059,12 +1059,6 @@ dependencies = [
  "wasm-bindgen",
 ]
 
-[[package]]
-name = "json"
-version = "0.12.4"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "078e285eafdfb6c4b434e0d31e8cfcb5115b651496faca5749b88fafd4f23bfd"
-
 [[package]]
 name = "language-tags"
 version = "0.3.2"
@@ -1416,7 +1410,6 @@ dependencies = [
  "actix-web",
  "bytes",
  "futures",
- "json",
  "lazy_static",
  "log",
  "pdf",