improvements in importing RTF texts with tables. Refs: #86.
\trgaph added
\trleft added
\pard ignored inside a table row
Every table row gets its own ruler now in \row. This ruler may be merged
with the previous ruler if there are no differences.

In addition, the handling of hyperlinks has been improved for better readability.

Signed-off-by: Josef Templ <josef.templ@gmail.com>