BLOB support for postgres, mysql and sqlite.

I've added support for binary data insertion into BLOB columns which addresses issue #140

Basically, any time you try to do an insert with a Buffer datatype, it will convert it into:

``` sql
INSERT INTO mytable (blobvalue) VALUE (x'DEADBEAF');
```
For mysql and sqlite.

And for postgres:
``` sql
INSERT INTO mytable (blobvalue) VALUE ('\xDEADBEAF');
```