resolves #564 & #936 - constrain subscript & superscript markup

- supscript & superscript only span non-whitespace characters
resolves #1005 use the term stem in favor of math
Merge pull request #1007 from mojavelinux/issue-564

resolves #564 & #936 - constrain subscript & superscript markup
resolves #717 disable single quotes as formatting marks for emphasized text

- disable single quotes as emphasis formatting marks by default
- introduce compat-mode document attribute to reenable legacy behavior
- add compat_mode property to document to set compatibility mode
- don't replace trailing single quote with right single smart quote
- introduce `' as the formatting mark to make a right single quote (rsquo)
- unescape escaped single quote explicitly
- update compat file for AsciiDoc Python
Merge pull request #1004 from mojavelinux/issue-717

resolves #717 disable single quotes as formatting marks for emphasized text
Merge pull request #1008 from mojavelinux/issue-1005

resolves #1005 use the term stem in favor of math
resolves #924 correctly calculate columns if colspan used in 1st row of table
resolves #789 add compliance setting for shorthand property syntax
Merge pull request #1009 from mojavelinux/issue-924

resolves #924 correctly calculate columns if colspan used in 1st row of table
Merge pull request #1010 from mojavelinux/issue-789

resolves #789 add compliance setting for shorthand property syntax
resolves #718 use + and ++ as constrained and unconstrained passthrough

- change + to be constrained passthough (no monospaced formatting)
- change ++ to be unconstrained passthrough (no monospaced formatting)
  * same as $$
- change ` to be constrained monospace (no passthrough behavior)
- change `` to be unconstrained monospace (no passthrough behavior)
- remove inline attributes from inline constrained passthrough
- use compat-mode document attribute to reenable legacy behavior
- update compat file for compatibility with AsciiDoc Python
- update tests for both compatibility modes