Use selector slicing in ADJACENT selector

[jleclanche]

In ADJACENT() and Rolling Boulder, we should use selector slicing which would make LEFT_OF and RIGHT_OF selectors select all minions to the left/right of the selector instead of just the first one.

[smallnamespace]

@jleclanche

How does that interact with child selectors that return multiple items? E.g. if we have:

1 2 X 4 5 X 7 8

where X is the child selector, then left currently picks out 2 and 5 -- you would prefer it selected the entire 1-5 range?

For example, LEFT_OF(X) evaluates to the same result as ALL_LEFT_OF(X)[-1] only in the case where X has a single element.