Folia-tools

* folia2html: Implemented support for render superscript/subscript 26
* folia2html: mplemented the ability to add custom external CSS stylesheets 26
* updated help info for fixunassignedprocessor procedure

Minor bugfix release:

* Fixes an issue in folia2salt (thanks to parkervg)

* [foliatextcontent] Fixed and improved substring linking, adding markup elements that reference substrings, also supports corrections 23

Minor update:

* [tei2folia] Better handling, detection and validation of IDs 22

Major performance improvement in foliasplit.

* [rst2folia] implemented rubric handling
* [foliasplit] Implemented a new tool to split a FoLiA document into multiple documents, based on a user's selection criteria. Also allows for linking from a parent document to external child documents. 20
* [foliaerase] Fixed the inability to properly handle markup elements 21