Specify PDF layers in Poppler utils CLI

Currently Poppler utils do not allow to specify layers when rendering PDFs from command line, nor list existing layers in pdfinfo. Suggestion is to provide command line argument to control layers. Controlling layers is absolutely necessary when using utils from the scripts.

Example:

pdfinfo -layers <all|off|on> - print layers tree available in the document, optionally filter them to display only visible/hidden.

pdftoppm -layer Foo -layer Hello/World -layer Bar/* - display only specified layers, slash "/" allows to separate hierarchy elements, wildcards could be used for the patterns. Additionally regexp could also be implemented for better controlling the layers filter.

I already have patch that does this, want to understand maintainer vision of such feature.