A single `read` function parsing pandoc-supported formats is added to
the module. This is simpler and more convenient than the previous method
of exposing all reader functions individually.
Filtering functions take element components as arguments instead of the
whole block elements. This resembles the way elements are handled in
custom writers.
Plain text readers are exposed to lua scripts via the `pandoc.reader`
submodule, which is further subdivided by format. Converting e.g. a
markdown string into a pandoc document is possible from within lua:
doc = pandoc.reader.markdown.read_doc("Hello, World!")
A `read_block` convenience function is provided for all formats,
although it will still parse the whole string but return only the first
block as the result.
Custom reader options are not supported yet, default options are used
for all parsing operations.
