Use px:epub3-create-toc in px:epub3-to-pef

[bertfrees]

(instead of http://www.daisy.org/pipeline/modules/braille/xml-to-pef/generate-toc.xsl).

The benefit is that we have more code reuse and also that the CSS can be made more "standard" (less specific to the epub3-to-pef script) because the generated TOC will be more standard. Also it will be able to handle a sequence of documents when we disable the HTML merge (see #195 and #93).

The downside is that it it will not be possible anymore to control the order between the TOC generation and other pre-processing the way it was done in daisy/pipeline#546. But then again, the "stylesheet" option isn't really meant for pre-processing anyway. It is meant for styling. Pre-processing should ideally be done before the script is called. Also we can of course keep "http://www.daisy.org/pipeline/modules/braille/xml-to-pef/generate-toc.xsl" available. (EDIT: Note that since 11a2169 it is already not possible anymore to control the order between the TOC generation and XSLT stylesheets. But currently the TOC generation always happens last, which, combined with the new option that was added in bc48e31 to exclude certain headings from the TOC, is the most flexible. If we move to px:epub3-create-toc it will probably mean the TOC generation is done before any XSLT stylesheets, so the "stylesheet" option should really not be used for pre-processing anymore.)