Fix some external links (#3157)

[xehrad]

I agree. I had tried to arrange the list in alphabetical order.

json-enc converts an HTML form into a simple {input.name: input.value} map, whereas form-json allows input.name values containing . to be interpreted as paths for nested structures.
It also supports <input type="file">, converting file inputs to Base64-encoded data.

json-enc

<form hx-ext="json-enc">
  <input name="user.age" value="18" type=number" />
  <input type="file" name="document">
</form>

<!-- Submission:
{
  "user.age":  "18"
}
-->

form-json

<form hx-ext="form-json">
  <input name="user.age" value="18" type=number" />
  <input type="file" name="document">
</form>

<!-- Submission:
{
  "user":  {
    "age":  18
  },
  "document": {
    "type": "application/pdf",
    "name": "file.pdf",
    "body": "SSBtdXN0IG5vdCBmZWFyLlxuRmVhciBpcyB0aGUgbWluZC1raWxsZXIuCg=="
  }
-->

Checklist

• [*] I have read the contribution guidelines
• [*] I have targeted this PR against the correct branch (master for website changes, dev for
  source changes)
• [*] This is either a bugfix, a documentation update, or a new feature that has been explicitly
  approved via an issue
• [*] I ran the test suite locally (npm run test) and verified that it succeeded