Add getters' support (keys like "getMyProperty()") to `ArrayHelper`

[vjik]

Q	A
Is bugfix?	❌
New feature?	✔️
Breaks BC?	❌
Fixed issues	#90

[codecov[bot]]

Codecov Report

Base: 99.49% // Head: 99.50% // Increases project coverage by +0.00% :tada:

Coverage data is based on head (3a36504) compared to base (5a43856). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #122 +/- ## ========================================= Coverage 99.49% 99.50% - Complexity 197 198 +1 ========================================= Files 5 5 Lines 397 401 +4 ========================================= + Hits 395 399 +4 Misses 2 2 ``` | [Impacted Files](https://codecov.io/gh/yiisoft/arrays/pull/122?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=yiisoft) | Coverage Δ | | |---|---|---| | [src/ArrayHelper.php](https://codecov.io/gh/yiisoft/arrays/pull/122?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=yiisoft#diff-c3JjL0FycmF5SGVscGVyLnBocA==) | `99.65% <100.00%> (+<0.01%)` | :arrow_up: | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=yiisoft). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=yiisoft)

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[samdark]

Need it described in README.