message: add more envronment
  add `definition`, `example`, `lemma`, `corollary` environments
diff: "flalignAst":{
  "text":"flalign*"
  },
  + "definition":{
  + "text": "definition"
  + }
  + "example": {
  + "text": "example"
  + }
  + "lemma": {
  + "text": "lemma"
  + }
  "theorem":{
  "text":"theorem"
  },
  + "corollary": {
  + "text": "corollary"
  + }
  "cases":{
  "text":"cases"
  },
  