[DAS2] Updated HTML get spec doc

[Steve Chervitz]

I just committed some updates to the das2_get.html document, so to all
editors out there, be sure to CVS update to get the latest version before
modifying.

I also updated the publically visible doc at
http://biodas.org/documents/das2/das2_get.html which normally gets updated
from CVS just once a day (not sure when).

Here's a summary of my changes:

  * Clarified description of half-open (interbase) intervals in section
    1.5 Segment ranges.  Reworded and added illustrative example.
    This numbering system may be a foreign concept to many.

  * Added some in-page links to some key sections (feat filters,
    global seq ids).

  * Removed the XXX in the third para along with the ambiguous
    sentence it was referring to. Seemed like unnecessary complication.

  * Added/fixed external links (form-urlencoded, textuality link)

  * Fixed some typos in the text, including one html glitch.

There are currently three remaining XXX comments: one pertaining to DAS
registry at Sanger, and two pertaining to alignments (which Gregg said he's
working on). Can someone in the know take a look at the comment re: the
Sanger registry in section 3.1?

Steve