Org reader: Slight cleaning of table parsing code
Org reader: use specialized org parser state

The default pandoc ParserState is replaced with the new
`OrgParserState`.  This will simplify the introduction of new state
fields required for efficient Org parsing.
Org reader: Fix parsing of nested inlines

Text such as /*this*/ was not correctly parsed as a strong, emphasised
word.  This was due to the end-of-word recognition being to strict as it
did not accept markup chars as part of a word.  The fix involves an
additional parser state field, listing the markup chars which might be
parsed as part of a word.