ChemSpiPyRateError: Too Many Requests;

Dear all,

After looping from my list of queries (45 in total), I repeated with more and got this error:

```
from chemspipy import ChemSpider
cs = ChemSpider('my_api_key')
c = cs.get_compound(2157)
print(c.molecular_weight)


ChemSpiPyRateError: Too Many Requests;
```

Any clue? looks like I reached the limit for my searches.
Bests