tail: Get the last lines of a file as the tail command

This class can be used to get the last lines of a file like the Unix tail command.

It can also filter the retrieved lines so only the lines that have a certain keyword or match a given regular expression are returned, like when using the Unix grep command.

It uses pure PHP commands so it can work on non-Unix like systems.

The maximum number of returned lines is configurable. The retrieved lines are returned as a text string. The retuned text may be highlighted or even formatted as an HTML list, or as XML document.