ext-iconv is missing as requirement

[tomasnorre]

Version: 3.1.1

Bug Description

I have a PHp 7.2 installed with no ext-iconv and this makes the Utils/Strings.php failing.

PHP Warning: Use of undefined constant ICONV_IMPL - assumed 'ICONV_IMPL' (this will throw an Error in a future version of PHP) in /home/tomasnorre/Projects/typo3/ext-crawler/crawler/.Build/vendor/nette/utils/src/Utils/Strings.php on line 150

The ext-iconv is a part of the suggested packages in composer, but to me it looks more like a hard requirement and not just a suggestion.

The might be reasons for this I don't know, perhaps windows computers.

Expected Behavior

I would expect the composer install to complain before getting installed if all requirements are not fulfilled.

[janpecha]

See #151 (comment)

[tomasnorre]

Hmm. Don't agree with that argument.

A functionality is a functionality regardless of how small of and edge case it is that uses another external component.

[tomasnorre]

Thanks