resolves #298 horizontal dlist layout in docbook backend
Merge pull request #340 from mojavelinux/docbook-horizontal-dlist

resolves #298 horizontal dlist layout in docbook backend
cleanups and minor improvements

- remove unused dependencies (mocha, htmlentities)
- use proper mimetype for SVG
- allow backend option to be specified as symbol
- set haml format to html5 for all html backends (including slides)
Merge pull request #343 from mojavelinux/cleanups

cleanups and minor improvements
resolves #313 honor haml/slim/jade-like shorthand for id and role attributes
Merge pull request #344 from mojavelinux/id-role-shorthand

resolves #313 honor haml/slim/jade-like shorthand for id and role attributes
resolves #321 move caption to AbstractBlock, assign even if no title
resolves #214 parse attributes in link when use-link-attrs is set
Merge pull request #346 from mojavelinux/link-attributes

resolves #214 parse attributes in link when use-link-attrs is set
document additional differences
Merge pull request #345 from mojavelinux/caption-cleanup

resolves #321 move caption to AbstractBlock, assign even if no title
resolves #175 block title not allowed above document title

- also fix dulicate warning when level 0 section appears in article
optimize split operations, remove unneeded constants
Merge pull request #347 from mojavelinux/block-title-above-doc-title

resolves #175 block title not allowed above document title
resolves #228 support {set:name:value} syntax

- also honor cellbgcolor for table cells
Merge pull request #348 from mojavelinux/split-optimization

optimize split operations, remove unneeded constants
Merge pull request #349 from mojavelinux/set-attribute-inline

resolves #228 support {set:name:value} syntax
resolves #350 shorthand syntax for table format
Merge pull request #351 from mojavelinux/table-format-shorthand

resolves #350 shorthand syntax for table format
resolves #122 link section titles

- add option sectanchors to add anchors to section titles
- add option sectlinks to turn section titles into links
- update stylesheet to display accordingly
- make .lead style available to AsciiDoc paragraphs