message: Added proposition and remark environments
  Similar environments are already there, like theorem and example.
diff: "example": {
  "name": "example"
  },
  + "remark": {
  + "name": "remark"
  + },
  "lemma": {
  "name": "lemma"
  },
  "corollary": {
  "name": "corollary"
  },
  + "proposition": {
  + "name": "proposition"
  + },
  "proof": {
  "name": "proof"
  },
  