Improve error classification

[ceddlyburge]

Most of the wordy exercise is satisfying to complete, but getting the errors correct at the end is very frustrating. The errors themselves seem organised in a non sensical way to me, and getting the tests to pass involves making the code worse, which seems like a bad lesson for a student.

I have hopefully improved the messages, so that:

• 'unknown operation' is for when you expected an operator (plus, minus etc), but didn't get one.
• 'syntax error' is for everything else.

I think another option would be to add a third type of error, for when you are expecting an integer, but don't get one, which I would also be open to.

@BethanyG

[glennj]

      "input": {
        "question": "What is 1 2 plus?"
      },
      "expected": {
        "error": "unknown operation"
      }

... unless you're a Forth programmer ;)

[iHiD]

(Cross reference to https://forum.exercism.org/t/educational-value-of-accidental-complexity-input-validation-case/3881)

[BethanyG]

For reference/additional context, below is a list of the exercises (that I know of)
that have some sort of error handling/raising/messaging:

Exercises with error handling cases

Exercise	Data
affine-cipher	canonical-data
all-your-base	canonical-data
bank-account
binary	canonical-data
binary-search	canonical-data
bowling	canonical-data
change	canonical-data
circular-buffer	canonical-data
collatz-conjecture	canonical-data
dot-dsl
error-handling
forth	canonical-data
go-counting	canonical-data
grains	canonical-data
hamming	canonical-data
hangman
hexadecimal
largest-series-product	canonical-data
meetup	canonical-data
minesweeper	canonical-data
nth-prime	canonical-data
nucleotide-count	canonical-data
ocr-numbers	canonical-data
octal
palindrome-products	canonical-data
perfect-numbers	canonical-data
phone-number	canonical-data
pov	canonical-data
queen-attack	canonical-data
saddle-points	canonical-data
satellite	canonical-data
say	canonical-data
series	canonical-data
sgf-parsing	canonical-data
simple-linked-list
tree-building
variable-length-quantity	canonical-data
wordy	canonical-data