ENH: add array format option function

[sasaki77]

This PR fixes #83.

arrayFormat function provides 3 types of array format: timeseries, index, and dt-space.

Assume that we have following array data:

[
    {
        "meta": {
            "name": "PV:NAME",
            "waveform": true,
            "PREC": "0"
        },
        "data": [
            {
                "millis": 1577804410000,
                "val": [
                    val1_1, val1_2, val1_3, val1_4, ..., val1_361
                ]
            },
            {
                "millis": 1577804510000,
                "val": [
                    val2_1, val2_2, val2_3, val2_4, ..., val2_361
                ]
            }
        ]
    }
]

Each format should return as following:

timeseries

time	PV:NAME[0]	PV:NAME[1]	...	PV:NAME[360]
1577804410000	val1_1	val1_2	...	val1_361
1577804510000	val2_1	val2_2	...	val2_361

index

index	2020-01-01T00:00:10.000Z	2020-01-01T00:01:50.000Z
0	val1_1	val2_1
1	val1_2	val2_2
...	...	...
360	val1_361	val2_361

dt-space

time	PV:NAME
1577804410000	val1_1
1577804410001	val1_2
...	...
1577804410360	val1_361
1577804510000	val2_1
1577804510001	val2_2
...	...
1577804510360	val2_361