Clean up HTML errors, part 1

 * Remove </input>
 * Remove </img>
 * Move alt attributes from div to img's
 * Correct _blanc to _blank
 * Remove some duplicate tags and attributes
Provide an example file for settings
composer updated
Rewrite variable parsing to avoid XSS attacks

 * Change $_SERVER['search'] to $search
 * Move some functions to a dedicated file in lib/
 * Create a file for initialization (i.e. loading other files, setting first vars)
 * Don't use _GET values directly, parse them first (prevent XSS attacks)
 * New functions: clean_text & process_GET
 * Minor whitespace changes