String Calculator

Adapted to Python from this kata.

Instructions

Create a simple string calculator with a method signature:
```
add(str numbers) -> int
```
The method can take up to two numbers, separated by commas, and will return their sum.
- for example '' or '1' or '1,2' as inputs.
- for an empty string it will return 0
Allow the add method to handle an unknown amount of numbers
Allow the add method to handle new lines between numbers (instead of commas).
- The following input is ok: '1\n2,3' (will equal 6)
- The following input is NOT ok: '1,\n' (not need to prove it - just clarifying)
Support different delimiters
- To change a delimiter, the beginning of the string will contain a separate line that looks like this:
```
    '//[delimiter]\n[numbers…]'
```
for example '//;\n1;2' should return 3 where the default delimiter is ';'.
- The first line is optional. All existing scenarios should still be supported
Calling add with a negative number will throw an exception "negatives not allowed" - and the negative that was passed.
If there are multiple negatives, show all of them in the exception message.

STOP HERE if you are a beginner. Continue if you can finish the steps so far in less than 30 minutes.

Numbers bigger than 1000 should be ignored, so adding 2 + 1001 = 2
Delimiters can be of any length with the following format:
```
'//[delimiter]\n'
```
for example: '//[***]\n1***2***3' should return 6

Allow multiple delimiters like this:
```
'//[delim1][delim2]\n'
```
for example '//[*][%]\n1*2%3' should return 6.
Make sure you can also handle multiple delimiters with length longer than one character