I just created another option because this is something I wanted as well but I cannot use the Compendium anymore.
You can now filter the entries to specific books (e.g., to create an Essentials only library) by creating a file named "Valid Sources.txt" in the same directory as the parser. All the valid sources from all entries are listed in "All Valid Sources.txt". Copy that and remove what you do not want. Only entries that match with one of the sources you list will make it into the final module. So if you want Essentials only, then list only the books/sources you consider "Essentials". Then parse all entries and only the ones matching those sources will appear in the module. Probably best use from a saved file that already has all the entries rather than downloading all entries again.
When you run the parser it should list how many entries pass the filter. For example:
25408 Total Entries
32190 Total Resulting Parsed Entries
Filtering
3026 Total Resulting Filtered Parsed Entries

