Ebookmaker

New formats: html.noimages and pdf.noimages.
No-image builds use a placeholder 'broken' image instead of nothing.
Figure directives without a filename create a placeholder 'broken' image.
New option :selector: in lof and lot directives for filtering.
Turn off italics with class no-italics (and bold with no-bold).
nbsp now works in ascii txt, soft hyphens now removed from ascii txt.
Insert line numbers with [ln 42] and [ln!42].
Works with kindlegen 2.0.

Allow unicode line separator U+2028 as line feed.
Fix XetexWriter bug with tables without explicit width.
Add language support in XetexWriter.

Fix line height of large text.
Fix images with spaces in src attribute.

Add image_dir to Xetex writer.
Use quotation environment instead of quote.
Don't automatically insert \frontmatter.
Page nos. for kindlegen 1.2.
Call kindlegen.
Integrate changes into PG environment.

Reduce vertical margin of images to 1 in TXT.
Fixed link targets in NROFF, PDF.
Report error on xetex errors.
Escape characters in PDF info.

Fixed crash on HTML comments in Kindle writer.