Bug report

Summary

When trying out the new MODX3 Alpha 2 I get the following error message on the set-up screenn:

Fatal error: Uncaught Error: Call to undefined function mb_split() in /home/mytest/public_html/core/vendor/smarty/smarty/libs/plugins/shared.mb_str_replace.php:47 Stack trace: #0 /home/mytest/public_html/core/vendor/smarty/smarty/libs/plugins/modifier.replace.php(34): smarty_mb_str_replace('[[+current_year...', '2020', '© 2005-[[+...') #1 /home/mytest/public_html/core/cache/setup/smarty/f408b021d2b46489800138ede826932f9da88e74_0.file.footer.tpl.php(37): smarty_modifier_replace('© 2005-[[+...', '[[+current_year...', '2020') #2 /home/mytest/public_html/core/vendor/smarty/smarty/libs/sysplugins/smarty_template_resource_base.php(123): content_5e37fe9d7cd3c4_44651287(Object(Smarty_Internal_Template)) #3 /home/mytest/public_html/core/vendor/smarty/smarty/libs/sysplugins/smarty_template_compiled.php(114): Smarty_Template_Resource_Base->getRenderedTemplateCode(Object(Smarty_Internal_Template)) #4 /home/mytest/public_html/core/vendor/smarty/smarty/libs/sysplugins/smarty_internal_template.php(216): Smarty_Template_C in /home/mytest/public_html/core/vendor/smarty/smarty/libs/plugins/shared.mb_str_replace.php on line 47

Step to reproduce

This appears to be because my server defaults to php v7.0.x which I know is no longer supported but couldn't we have a check in place for this to warn the user instead as if anyone new is trying out MODX for the first time, it's not the most welcome of starts.

Observed behavior

Error as above.

Expected behavior

PHP < 7.2 I should see a warning message that older versions are not supported and I should upgrade.
PHP >= 7.2 I should see the lovely new installation page.

Environment

Ubuntu server
Apache 2.x
Php 7.0.x

This works correctly when I switch to PHP 7.2.

Thanks!