Allow selection of specific files to be exported

[cesaremorel]

Hi, thanks for your great job!

It would be great to have the chance to select specific files to be exported.

Selection could be based on regular expressions, a specific folders, or even in a session variable.

[glenux]

Same problem here. It seems mkdocs-pdf-export-plugin exports all the files it sees without respecting my existing file selection.

In my case the site tree is built automatically based on the https://github.com/lukasgeiter/mkdocs-awesome-pages-plugin plugin which allows to define the order, the tree, page filters with regexp, etc... and mkdocs-pdf-export-plugin does not care about the tree structure and the chosen titles.

It would be great if both plugins could work together!