RTL support draft

[nicStuff]

Incomplete RTL (right-to-left) support (requested in #207) for half-stars on mouse over. For being considered complete it still needs at least the following:

• half-stars horizontal flipping, for instance

[dir='rtl'] div.rating .star-half {
	transform: scaleX(-1);
}

• reversing the stars as mentioned in the issue, like

div.rating {
  display: flex;
  flex-direction: row-reverse;
}

I have tested these changes on an older version of the library and they seem to work; however I did not test all the use cases, and it would be nice to include the CSS sets in the raty plugin itself instead of relying on external CSS.