:Sample Code:
    .. code-block:: python
        :caption: Write a Markdown table with a margin

        import pytablewriter

        writer = pytablewriter.MarkdownTableWriter()
        writer.table_name = "write example with a margin"
        writer.header_list = ["int", "float", "str", "bool", "mix", "time"]
        writer.value_matrix = [
            [0,   0.1,      "hoge", True,   0,      "2017-01-01 03:04:05+0900"],
            [2,   "-2.23",  "foo",  False,  None,   "2017-12-23 45:01:23+0900"],
            [3,   0,        "bar",  "true",  "inf", "2017-03-03 33:44:55+0900"],
            [-10, -9.9,     "",     "FALSE", "nan", "2017-01-01 00:00:00+0900"],
        ]
        writer.margin = 1  # add a whitespace for both sides of each cell

        writer.write_table()

:Output:
    .. code-block:: none

        # write example with a margin
        | int | float | str  | bool  |   mix    |           time           |
        |----:|------:|------|-------|---------:|--------------------------|
        |   0 |  0.10 | hoge | True  |        0 | 2017-01-01 03:04:05+0900 |
        |   2 | -2.23 | foo  | False |          | 2017-12-23 12:34:51+0900 |
        |   3 |  0.00 | bar  | True  | Infinity | 2017-03-03 22:44:55+0900 |
        | -10 | -9.90 |      | False |      NaN | 2017-01-01 00:00:00+0900 |

``margin`` attribute can be available for all of the text format writer classes.
