Add "--align" flag to table command.

[alex-ozdemir]

This flag allows the user to specify how data should be aligned within columns. The options are:

• left
• right
• center

This alignment is applied to all columns.

Per the tabwriter crate, center alignment breaks ties in favor of being closer to the left. Thus if "hi" appears in a column of width 5, it will be printed as " hi ".

resolves #165.