supports specifying alternative time_precision

You can now specify the time resolution for queries and writing points using the `--time_precision s|ms|u` flag. 

Eg:

```
$ be bin/influxdb-cli db --time_precision u --pretty
Connecting to {"host"=>"localhost", "port"=>8086, "username"=>"root", "password"=>"root", "database"=>"db", "ssl"=>false, "time_precision"=>"u", "pretty"=>"pretty"}
✔ ready
[1] pry(main)> use test
[2] pry(main)> SELECT * FROM /.*/ LIMIT 1
+----------------------------+-----------------+-------------+
|                            test                            |
+----------------------------+-----------------+-------------+
| time                       | sequence_number | message     |
+----------------------------+-----------------+-------------+
| 2014-12-19 05:46:41.787520 | 10001           | Hello Pablo |
+----------------------------+-----------------+-------------+
1 result found for test

Query duration: 0.0s
[3] pry(main)> quit
```