Marshal custom config types as JSON

[markphelps]

Builds off of #1027, will rebase once thats merged

Implements MarshalJSON for config types (uint8)

Before

{
  "log": {
    "level": "DEBUG",
    "encoding": 1
  },
...
  "cache": {
    "enabled": false,
    "ttl": 60000000000,
    "backend": 1,
    "memory": {
      "evictionInterval": 300000000000
    },
}

After

{
  "log": {
    "level": "DEBUG",
    "encoding": "console"
  },
 ...
  "cache": {
    "enabled": false,
    "ttl": 60000000000,
    "backend": "memory",
    "memory": {
      "evictionInterval": 300000000000
    },
}