'Downgrade' / support older versions of PHP

[nfreear]

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• — Remove namespace declarations;
• — Older array( ) syntax ~ http://php.net/manual/en/migration54.new-features.php
• — Add to .travis.yml;

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• http://php.net/ChangeLog-5.php#5.2.2 ~ released, 03 May 2007;
• http://php.net/manual/en/language.namespaces.rationale.php ~ PHP 5 >= 5.3.0, PHP 7;
• http://php.net/supported-versions.php
• http://php.net/eol.php ~ PHP 5.2 end-of-life: 6 Jan 2011;

..

• HTML to Markdown: https://browserling.com/tools/html-to-markdown

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