Handle "." (dot) as the grid area name

[kettanaito]

What

Need to handle . character which is supported by CSS Grid spec.

Why

In order to cover feature which is in spec, in case it needs to be handled from React side.

How

1. Refine what dot stands for in grid-template-areas. There is a fair chance that we need not to handle it in any way. If that is a placeholder to achieve different gutter (gap) between different grid areas, this can be done via explicit spacing props (margin/padding) assigned directly to area components as props.
2. If it's a placeholder, it can be handled by rendering a <Placeholder/> component at its place.

[kettanaito]

It seems that dot is there to create an empty row/column to achieve uneven gutter (gap).

If it's so indeed, the same result can be achieved using padding/margin properties applied to specific grid areas, no need to handle that on the template level. But I would like to make sure I understand the dot's behavior properly.

[kettanaito]

Verified as a part of #56. Citing:

Period (.) seems to be handled properly.
In case unexpected behavior is encountered, a respective issue should be created.

Closing.