Ebookmaker

- fix error when a style element is empty
- fix error when style contains non-ascii text
- fix issue with aux files not being copied to html destination
- use secure version of Pillow

- fix reversion in 0.11.10 leaving out added meta elements
- remove encoding meta element originating in HTML5 source from EPUB2 files, as it was causing validation failures.
- remove media handheld rules for HTML
- move content of table summary attribute to data-summary attribute
- width attribute on table and col is converted to css in a style attribute
- non-integer width or height on img is converted to css in a style attribute
- fixed epub builds for books with images in external css sheets
- the 'big' element is obsolete; changed to <span class="xhtml_big">. css is altered or added as appropriate
- a number of table attributes are obsolete in html5 and changed to the corresponding css styles: tablewidth, colwidth, tablecellpadding, tablecellspacing, tableborder, tdalign, thalign, tdvalign, thvalign
- html5 doesn't allow elision of dd in dl. Where they are missing, we add empty dd
- html5 doesn't permit carriage returns. these are replace by newlines when represented as numeric entities.
- libgutenberg dependency updated to 0.8.11
- fix issue of polymorphism in dc.languages. Without a db, it's a list of structs; with a db, its a related collection.
- ebookmaker will no longer ignore xml:lang or DC meta attributes
- fix windows path comparison - ebookmaker will behave properly when input file is in outputdir

- remove encoding meta element originating in HTML5 source from EPUB2 files, as it was causing validation failures.
- fix bug when an XHTML source file set an xml:lang attribute

- use tidy for _all_ html source files
- addressed long-standing issue where images referenced in css were not included in epubs. This issue surfaced because the images were also missing from generated files.
- addressed some simple issues preventing derived HTML5 files from validating. More complex issues involving incompatibilities between XHTML and HTML5 have been enumerated and will be addressed in subsequent updates.
- removed http-equiv meta elements for Content-Type and Content-Style-Type
- set lang attribute when xml:lang attribute is present
- removed duplicate encoding meta elements introduced by HTML5 source.
- removed type attribute from style elements
- update requirements so that stand-alone installs will work better

- more aggressive session closing