Add simple "markdown" target table format

[meinsiedler]

Add support for markdown tables which look like this:

| Tables | Are  | Cool |
| ------ |------| -----|
| 1      | 2    | 3    |
| 4      | 5    | 6    |
| 7      | 8    | 9    |

Notes:

1. Since most of the markdown parsers do not support tables without headers, the first row will always be a header row.
2. Alignment of columns is not supported in the first step.
3. Pretty printing is also not implemented in the first step. (see Add "Pretty print" option for all output formats #12)