Configure manual to be processed with mk4ht,

With these modifications the file can be processed with mk4ht and HTML output is generated. The HTML can be processed with Calibre and converted to EPUB or MOBI ebook formats.

Command line for conversion:

mk4ht htlatex Slic3r-Manual.tex 'xhtml,charset=utf-8,pmathml' ' -cunihtf-utf8 -cvalidate'

Please, consider this commit on future versions.

Best regards,
Benito