only print hasOwnProperty properties

Tests still pass.

I made this change in my fork because I am using the `mysql` package and it returns an array of row object.  When I did `Table.printArray(rows)` I got a bunch of noise, as each row has a `.parse` and `._typecast` function.  The output included the source of these functions.

This change only prints own properties, which is typically what I think is desired.  This could, of course, be made an option though.

An additional enhancement might be to by default only print something like `[Function: parse]` (using `util.inspect`) instead of the source code.