Make it possible to process yaml instead of json

[tumdum]

Adds new flag that tells gron to treat input as a yaml instead of json. So that I don't have to use external tools to convert to json first :)

[FreedomBen]

Implementation like clean, and it even has tests. I hope a maintainer will consider merging this.

[jmcantrell]

Adds new flag that tells gron to treat input as a toml instead of json. So that I don't have to use external tools to convert to json first :)

Title/code says yaml, but you say toml. The ability to process toml as well too would be nice, though.