Erik Nordström d87a6ee5a0 Allow partitioning in only time dimension
This allows creating hypertables as follows:
```
CREATE TABLE only_1dim(time timestamp, temp float);
SELECT create_hypertable('only_1dim', 'time');
INSERT INTO only_1dim VALUES('2017-01-12T08:11:03', 23.4);
```

It is implemented by making the specification of a partitioning column
optional, and when NULL the number of partitions will be set to 1.
2017-01-26 11:57:22 +01:00
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