fix typo Markdown->GithubMarkdown in $flavors['gfm-comment']

Improved checks where substr_compare is used, replaced more substr + comapre cases with substr_compare

fixes #4105, close #4376

Fixes #4318: `yii\helpers\Html::ul()` and `ol()` will return an empty list tag if an empty item array is given

1. Added proper handling and support of the symlinked directories.
2. Added $options parameter.

issue #746

issue #746

issue #746

- Added protected `\yii\Inflector::transliterate()` that could be replaced with custom translit implementation.
- Added proper tests for both intl-based slug and PHP fallback.
- Removed character maps for non-latin languages.
- Improved overall slug results.
- Added note about the fact that intl is required for non-latin languages to requirements checker.

Fixes #3358: Removed automatic CSRF meta tag generation by `View`. Added `Html::csrfMetaTags()` and its call to main layout files

fixes #3245, #3244