In particular when configured to replace several ranges with multiple fonts.

Given the following `font-codepoint-map` config:

```
font-codepoint-map=U+0030-U+0039=Monaco       # 0-9
font-codepoint-map=U+0040=mononoki            # @
font-codepoint-map=U+0041-U+005a=Pixel Code   # A-Z
font-codepoint-map=U+0061-U+007a=Victor Mono  # a-z
```

I noticed a couple of unexpected behavior:

1. Codepoint ranges were assigned the wrong font
2. The declaration order had a direct impact on the font assignment
   (seemed to be rotating in some fashion)

If my understanding of the current implementation is correct, for a
given range index `n` in the `MultiArrayList` `CodepointMap.get(…)`
returns the font descriptor at index `len - n - 1`. In other words, it
returns the descriptor symmetrically opposite relative to the middle of
the list.

I've added a couple test cases that I would expect to pass if my
understanding of the expected behavior is correct, verified that they
were broken under the current behavior, and updated the implementation
of `CodepointMap.get(…)` accordingly.

My understanding of the original intent is to give priority to the
latest range match in the list (which is a use case already tested by
the `codepointmap` test, but which I believe happened to pass "by
accident"), so I opted for a reverse traversal of the codepoint list.