Function createErrorMessage

createErrorMessage(src, errorStack): undefined | string
Convert a stack of errors to a string.
Parameters
- src: string
  
  the source string you tried to parse
- errorStack: DeadEnd<Ctx, Err>[]
  
  the stack of errors that occured when parsing the source string
Returns undefined | string
undefined if the stack of errors was empty, otherwise a string with the error message
Example
If we have the following invalid JSON:
```
{
 "a": "b
}
```
We get the following error message:
```
Cannot parse this value.

2|      "a": "b
               ^
Expected a double quote: "
```
- Defined in core.ts:250