resolves #612 generate data uri for remote image

- generate data uri for remote image when data-uri & allow-uri-read are set
- add content-type logic to test webserver
- minor optimizations
resolves #861 add source map information to blocks
Merge pull request #1015 from mojavelinux/issue-612

resolves #612 generate data uri for remote image
resolves #956 fix invalid docbook when adding role to formatted text

- add role attribute directly to literal, superscript and subscript elements
- update AsciiDoc compat file with the same changes
resolves #927 use informalfigure if block image doesn't have a title
Merge pull request #1017 from mojavelinux/issue-956

resolves #956 fix invalid docbook when adding role to formatted text
resolves #931 wrap <para> around admonition inside example block in DocBook 4.5
Merge pull request #1018 from mojavelinux/issue-927

resolves #927 use informalfigure if block image doesn't have a title
Merge pull request #1019 from mojavelinux/issue-931

resolves #931 wrap <para> around admonition inside example block in DocBook 4.5
resolves #961 warn if table without a body is converted to DocBook
Merge pull request #981 from mojavelinux/issue-961

resolves #961 warn if table only no body rows
Merge pull request #865 from mojavelinux/issue-861

resolves #861 add source map information to blocks
add note about disabling single quoted emphasis
add test for escaping unconstrained formatting marks

- add test for escaping unconstrained formatting marks
- use interpolation to insert backslash in test cases to be sure it's right
fix tests in Ruby 1.8.7
set default subs on stem block

- set default subs on stem block as [:specialcharacters]
- remove redundant whitespace stripping in stem block
- minor code optimizations
resolves #1022 \ as line continuation character in attribute value

- \ as line continuation character in attribute value
- join lines on endline char if preceding line ends with line break sequence
- optimize line continuation parse logic
Merge pull request #1023 from mojavelinux/issue-1022

resolves #1022 \ as line continuation character in attribute value
stage logic to restore passthroughs recursively; minor optimization
resolves #1024 don't clobber outfilesuffix attribute if locked