XProc optional steps in Componize

Componize implements the optional p:exec and p:xsl-formatter steps to allow external commands and XSL-FO processing.

Runs an external command passing the input that arrives on its source port as standard input, reading result from standard output, and errors from standard error.
Receives an XSL 1.1 document and renders the content. The result of rendering is stored to the URI provided via the href option. A reference to that result is produced on the output port.