Implement a function, so it will produce a sentence out of the given parts.
Array of parts could contain:
- words;
- commas in the middle;
- multiple periods at the end.
Sentence making rules:
- there must always be a space between words;
- there must not be a space between a comma and word on the left;
- there must always be one and only one period at the end of a sentence.
**Example:**
def make_sentences(parts):
    result = ''
    for i in range(len(parts) - 1):
        result += parts[i]
        if parts[i + 1] not in '.,':
            result += ' '
    result += parts[-1]
    return result.rstrip('.') + '.'
def make_sentences(parts):
    result = ''
    for i in range(len(parts) - 1):
        result += parts[i]
        if parts[i + 1] not in '.,':
            result += ' '
    result += parts[-1]
    return result.rstrip('.') + '.'