Issue 110

Bug related to `pgator-backend`:
* Dependency on `pgator-backend-0.1.2`. `PGNumeric` is now considered as a native type.
* If numeric cannot be represented as `double` then value is stored in string. Thus there are possible heterogeneous arrays of numerics:
```D
[1,
"20000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000",
3]
```