properly map between html and dtbook lists

fixes #55
fixes #56
closes #97
Merge branch 'issue-35-55-56-96-97'

fixes #96
closes #35
fixes issues with lists, as well as some assertions (issues 107/108/110)

 * allow list items to have the value attribute!
 * epub_nordic_127: check all ancestors for frontmatter or backmatter fixes #107
 * invert assertion tpb143. fixes #108
 * pf:numeric-alpha-to-decimal only works for single characters. Added implementation for multiple characters. fixes #110
   * added test for ordered list items using characters where multiple characters are present
 * dtbook-legacy-fix.xsl: always set track:Guidelines to 2011-2
Merge branch 'issue-107-108-110'
minor update to README

[skip ci]
DTBook imggroup with only one image will not be wrapped in image-series

 * added RNG restriction: image series must have at least two images
 * DTBook imggroup with only one image will not be wrapped in image-series
 * updated xslt tests
Merge pull request #112 from nlbdev/issue-57

DTBook imggroup with only one image will not be wrapped in image-series
use "-" in navdoc for unnumbered pages and fix imggroup/figure content model

fixes #58
fixes #95

 - nordic-html5.rng
   - allow both div and span for pagebreaks in figures
   - require pagebreaks and prodnotes to be placed after the image in image figures
   - disallow trailing pagenums and prodnotes in image-series; they must be placed before all the image figures

 - nordic2015-1.sch
   - added suffix to difference nordic253 assertions for easier distinction (a,b,c,d)
   - assert that there is at least 2 image figures in a image-series
   - added nordic260a: The first element in a figure with class="image" must be a "img" element
   - added nordic260b: Content not allowed between or after image figure elements

 - dtbook-to-epub3.xsl
   - fixed imggroup/figure mapping (see #95)
   - only add title attribute to pagenum if the pagenum has a value (allows for unnumbered pages)
   - page type set to "special" if unnumbered

 - epub3-to-dtbook.xsl
   - fixed imggroup/figure mapping (see #95)

 - updated tests and test resources in order to test and be valid against #58 and #95
 - removed epub3-nav-utils (it's now included in the main dp2 distro)
Merge pull request #114 from nlbdev/issue-58-95

use "-" in navdoc for unnumbered pages and fix imggroup/figure content model
dtbook-to-epub3: don't indent epub3 output

fixes #94

we can re-enable output indentation when (and if) daisy/pipeline-modules-common#69 is fixed
Merge pull request #115 from nlbdev/issue-94

dtbook-to-epub3: avoid trailing whitespace by don't indenting epub3 output
fixed test in dtbook-to-epub3.xsl resulting in bad pagebreaking

fixes #113
Merge pull request #116 from nlbdev/issue-113

fixed test in dtbook-to-epub3.xsl resulting in bad pagebreaking
fix for epubcheck reports and temporary fix for HTM-047 viewport issue

 * deleting HTM-047 errors (see #111)
 * prettier epubcheck HTML reports (as well as more in line with validator.idpf.org)
 * sorted epub:type/class/element usage statistics
 * fixed parsing of epubcheck XML reports
Merge pull request #117 from nlbdev/issue-111-tempfix

fix for epubcheck reports and temporary fix for HTM-047 viewport issue
translated default headlines for sectioning elements, tests for cover

 - added translations for untitled sections (en, no, sv, fi, da)
 - fixed assertion in nordic2015-1.opf.sch requiring cover to be secondary in spine
 - allow section without headline only in cover
 - generate headlines for use in the navigation document when headlines are missing
 - dtbook-legacy-fix.xsl: don't allow jacketcopy, precedingemptyline, precedingseparator, byline, dateline
 - epub3-to-dtbook.xsl: allow classes: frontcover, rearcover, leftflap, rightflap
 - added cover to test documents (DTBook, single-document XHTML, EPUB3) and updated tests accordingly

fixes #92
Merge pull request #118 from nlbdev/issue-92

translated default headlines for sectioning elements, tests for cover
added test for converting sidebar to figure when render is required

closes #69
closes #70
Merge pull request #120 from nlbdev/issue-69-70

added test for converting sidebar to figure when render is required
Make sure the p class "indented" is preserved

closes #72
fixes #73