resolves #113 cache default command on build config object

resolves #112 add stderr control to build command; include option to route messages to Antora logger

resolves #112 add stderr control to build command; include option to route lines to Antora logger

resolves #117 prefer site URL over primary site URL when producing absolute URLs

resolves #118 prepend link: prefix to resource reference with root-relative URL

resolves #100 introduce embedReferenceStyle on converter to control how image references are rewritten

resolves #100 introduce embedReferenceStyle on converter to control how image targets are rewritten

resolves #120 create internal link from duplicate nav entry to first occurence

resolves #122 assign intrinsic attributes assembler-filetype and assembler-filetype-<filetype>

resolves #116 introduce linkReferenceStyle configuration key to control how linkable targets are rewritten

resolves #116 introduce linkReferenceStyle configuration key to control how linkable targets are rewritten

resolves #119 support assembly-navtitle override for doctitle when root level is 1

resolves #115 export getDefaultCommand on converter for exporter to supply default command

resolves #25 introduce drop_explicit_xref_text key to control when Assembler drops text of xref