REG_template: Template engine that uses regular expressions

This class implements a template engine that uses regular expressions to locate and replace the template marks.

It takes a template file from a given directory and can search and replace marks with assigned variable values.

The class also supports literal sections with content that will not be processed as template marks, including external template files, conditional sections, iterate over sections multiple times, sections with explicit PHP code, and caching the processed template output for a given period of time.