Add prefer-lookaround rule

[ota-meshi]

This PR adds prefer-lookaround rule.

There is a problem that the behavior may be different if you replace it with "lookaround" as you said. To avoid this problem, I implemented to exclude complicated patterns from the check.

This rule is only checked if the pattern consists only of Character, CharacterClass, CharacterSet, CapturingGroup, Group, and Quantifiers max <= 10.
It also controls not to report, when the start capturing group, end capturing group, and the patterns between them include those that can match each pattern.
I think the implementation of this rule can have a lot of false negatives, but I think the rule is useful as far as I can think of at this point.

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close #183

[RunDevelopment]

I will do a full review soon. Here are a few minor things until then.

[RunDevelopment]

Sorry for the wait.

I have a few questions about the general approach you take:

1. What does CharSetTreeRoot.includes check? I don't understand which property we check here.
2. Can CharSetTrees grow exponentially in size? Let's say I have (?:a|a|a|a){10}. Will I get 4¹⁰=1M CharSetTree instances?

I also have a suggestion for another criterion for lookbehinds:

Let's say we have a capturing group g that is a candidate to become a lookbehind (it's the first capturing group, replace string starting with $1, etc). Let c be the union of all characters that can be consumed by g. We now go through all single-character elements (no quantifiers, groups, etc) after g. If any of those characters is disjoint with c, then we can replace g with a lookbehind.

Example: "".replace(/(a)Java/g, '$1foo') (this isn't replaceable with the current implementation.)

[ota-meshi]

Thank you for your review. I found that my method didn't work.
The method you suggested is very simple and works well! I have updated this PR to use that method.

[ota-meshi]

I changed this PR. Please check it again.

[ota-meshi]

I fixed the remaining issue. But coveralls seem to be down😅. I will need to re-run later.

[RunDevelopment]

LGTM;