Added basic error reporting

[Noble-Mushtak]

In this pull request, I added some basic error reporting, where, if jsonValue is unable to parse the given String, then it reports an error saying how many characters it had read in from the String when it encountered the problem, what it was expecting at that character, and what it actually found. For right now, the error reporting is pretty basic, as only charP, stringP, and parseIf actually report error messages. Here is an example:

*Main> runParser jsonValue "1e-s"
Right (1,"e-s",JsonNumber 1.0)
*Main> runParser jsonValue "[1e-s]"
Left (KnownError (2,"Expected ']', but found 'e'"))

In the first command, the jsonValue successfully parses the number 1 and then leaves the e-s alone because that exponent part is invalid. However, when we run jsonValue on an array containing 1e-s, it says we expected a ] when they found the e. Arguably, it should actually say that the exponent part of the number is invalid, but I think this will require some more complex error handling.

Also, as shown above, I report the number of characters the parser has read in so far. However, I had trouble figuring out how to get the number of characters that reads had parsed, since jsonNumber was implemented using reads. (One way to do this was to subtract the length of the whole string by the length of the unparsed input that reads returned, but this solution is O(n) where n is the length of the string, which I think is pretty inefficient and clunky.) Therefore, I rewrote jsonNumber based off the JSON Data Interchange Syntax, so that it could use charP, parseIf, and spanP, which makes it easier to update the number of characters read in so far.

[rexim]

@Noble-Mushtak hey! Thank you very much for the contribution! 👍