Better Error Messages

[FourierTransformer]

While I tried to make them rather good, I feel like sometimes the error messages are a little hard to understand, likely due to using a state machine, and they can be especially confusing when the error just prints the next 50 chars...

Ideas to make errors better:

• Highlighting the position in a row
• Indicating the key if there's a validation issue with a value

Any other ideas to make error messages better would be helpful!

[FourierTransformer]

While cleaning up the encoder codebase, came across this one:

lua: ./tinytoml.lua:152: In encode process line 1.1.0: Too many days in the month. Found 32 days in month 5, which only has 31 days in: 1979-05-32

         See https://toml.io/en/v#local-date for more details

[FourierTransformer]

A quick win that I think has been working rather well it to print the actual line out and then the error and trying to add as much context as possible. Still trying to figure out what to do with the encoder...

Progress is in #14