Emacs parses org documents into a tree structure, which is then
post-processed during exporting. The reader is changed to do the same,
turning the document into a single tree of headlines starting at
level 0.
Fixes: #3695
Parsing of smart quotes and special characters can either be enabled via
the `smart` language extension or the `'` and `-` export options. Smart
parsing is active if either the extension or export option is enabled.
Only smart parsing of special characters (like ellipses and en and em
dashes) is enabled by default, while smart quotes are disabled.
This means that all smart parsing features will be enabled by adding the
`smart` language extension. Fine-grained control is possible by leaving
the language extension disabled. In that case, smart parsing is
controlled via the aforementioned export OPTIONS only.
Previously, all smart parsing was disabled unless the language extension
was enabled.
Source block parameter names are no longer prefixed with *rundoc*. This
was intended to simplify working with the rundoc project, a babel
runner. However, the rundoc project is unmaintained, and adding those
markers is not the reader's job anyway.
The original language that is specified for a source element is now
retained as the `data-org-language` attribute and only added if it
differs from the translated language.
The line-numbering switch that can be given to source blocks (`-n` with
an start number as an optional parameter) is parsed and translated to a
class/key-value combination used by highlighting and other readers and
writers.
