Override WordPress template files.

template-functions.php

<?php
/**
 * Template loader.
 *
 * The template loader will check if WP is loading a template
 * for a specific Post Type and will try to load the template
 * from out 'templates' directory.
 *
 * @since 1.0.0
 *
 * @param string  $template Template file that is being loaded.
 * @return  string          Template file that should be loaded.
 */
function PLUGIN_template_loader( $template ) {

  $find = array();
  $file = '';

  if( is_singular() ):
    $file = 'single-plugin.php';
  elseif( is_tax() ):
    $file = 'archive-plugin.php';
  endif;

  if ( file_exists( PLUGIN_locate_template( $file ) ) ) :
    $template = PLUGIN_locate_template( $file );
  endif;

  return $template;

}
add_filter( 'template_include', 'PLUGIN_template_loader' );