Removing crsURN

This makes all GeoJSON objects Geographic/WGS84 in longitude, latitude order.
Merge pull request #6 from tschaub/crs-free

Removing crsURN
More narrative introduction.
Merge pull request #13 from sgillies/intro-narrative

Reworking the introduction
Change affiliation of S. Gillies.
Introduction improvement and addition of its cited references.

I think this better explains what a feature is and I've tried to format
it as much like RFC text as possible to get my mind around that. The
4 references cited in the intro have been added to the top of the
back section.
Make citations match references.
Moved GeoJSON-spec to normative refs, others to info refs.

Also, fix for xml2rfc bug:
http://trac.tools.ietf.org/tools/xml2rfc/trac/ticket/190#comment:3
Change LinearRing to linear ring.

I feel like this makes it less of a concrete thing.
More simplification and text formatting.

Consolidation of a few paragraphs, elimination of usused defs (see #9),
removal of discussion notes (see #10). Text width set to 72 chars to
roughly match the text output.

Added: specification that optional altitude is meters above the WGS 84
reference ellipsoid, something to be discussed and affirmed or
removed.