`jsontoml` is very similar to `tomljson`
It uses json.Unmarshal to convert read json to map and then
converts the map to tree using `toml.TreeFromMap`.
Then this tree is converted to toml using `tree.toTomlString()`
The numbers when taken as input from json get converted to float64
because of how `json.Unmarshal()` converts all json numbers to float.
Fixes#280
Thomas Pelletier