#15: dropped support of consecutive LNs and simplified sanitization algorithm.

- #LNTYPE 2 consecutive LN behavior is removed.
- sanitization algorithm will always keep only one type of most importance,
  with an exception of BOMB (which can be overlapped with INVNOTE).
- parser still guarantees that every LNSTART has LNDONE somewhere behind it.
- overlapping LNSTART/LNDONE is explicitly checked to avoid stranger result.
  consequently LNSTART/LNDONE order is no longer important.

--HG--
branch : 2.0
updated documents for consistent terms, acknowledgements and changes in #15.

note to translators: you are *strongly* advised to use wdiff for this change.

--HG--
branch : 2.0