':param headers_str: A string with the HTTP headers, example:
Server: Apache
Content-Length: 123'

@classmethod
def from_string(cls, headers_str):

    res = []
    split_str = headers_str.split('\r\n')
    for one_header_line in split_str:
        if (not one_header_line):
            continue
        (name, value) = one_header_line.split(':', 1)
        value = value[1:]
        res.append((name, value))
    return cls(res)
