Filenames with underscores or dashes not handled when reading saved.md

[chrispcampbell]

With the changes I made in #48 to switch to Markdown format for the saved files, I delineated pages with a marker like this:

<!-- BEGIN-PAGE[guide/transport_ee.md] -->

The problem is that the readSavedMarkdownContent function has a regex that doesn't allow for underscores or dashes in the filename, so if a page file has one of those characters, it will fail to match, and the page won't be included.

We need to fix the regex to allow for underscore and dash characters.