New truncate and truncateWords methods

New truncate and truncateWords methods, https://github.com/yiisoft/yii2/issues/2941
Update BaseStringHelper.php

Length check.
Update CHANGELOG.md
Update BaseStringHelper.php

Updated to use mb_* functions
Test case for new truncate methods.

Test case for new truncate methods.
Update BaseStringHelper.php
Fixes #2939: documented the process of creating your own application template
Updated data-grid.md to fix wrong path to GridView

Path was wrong
Merge pull request #3156 from acorncom/fixed-data-grid-docs-error

Updated data-grid.md to fix wrong path to GridView
Added `yii\web\UrlManager::addRules()` to simplify adding new URL rules
Fixes #2837: Error page now shows arguments in stack trace method calls
Fixes #3088: The debug and gii modules will manage their own URL rules now
Fixes #3158
fixed typo. [skip ci]
Fix typo
Merge pull request #3160 from marsuboss/patch-1

Fix typo
Added title for trimmed strings
Merge branch 'master'

Conflicts:
	framework/CHANGELOG.md
Merge pull request #3157 from yiisoft/exception-display-arguments

Fixes #2837: Error page now shows arguments in stack trace method calls
Update basics.md

I think, the correct form is `should be defined` OR `is defined`, but not `be defined`