Add YAML support

[Livven]

First off, thanks for this polished library.

Since YAML is compatible with JSON, it would be nice if there was an option to use YAML for the error visualization, i.e. instead of this:

  4 |   "content": [
  5 |     {
> 6 |       "type": "paragarph",
    |               ^^^^^^^^^^^
  7 |       "content": [
  8 |         {
  9 |           "type": "text",

Show this:

  4 |   content:
> 5 |     - type: paragarph
    |             ^^^^^^^^^
  6 |       content:
  7 |         - type: text

[sjaugmented]

Second this, mainly for the js formatting so I can use it as a codemirror linter.

[plocket]

I could really use this too. My data is all in YAML. When I'm looking at the error object, accurate line numbers would help. I'm not sure how/if it could be done, though.