Fix typos in XLink references
Fix broken XLink references

These local references are broken and their UUIDs don't exist anywhere
in the Donlon dataset.  We are replacing these by abstract references
for now, to restore the referential integrity of the XML document at
least formally.
Fix missing gml:identifier in a VerticalStructure
Remove sequenceNumber from SNAPSHOT

AIXM Temporality 1.0, page 9:

| Note that for a SNAPSHOT, the correctionNumber and the
| sequenceNumber properties shall not be populated.

http://www.aixm.aero/gallery/content/public/AIXM51/AIXM%20Temporality%201.0.pdf#page=9
Add missing "uuid." prefix to gml:id

AIXM Feature Identification and Reference 1.0, page 7:

| It is recommended that the gml:id of the AIXM features (such as
| aixm:Airspace, aixm:Runway, etc.) also make use of the UUID value,
| prefixed with "uuid.".

http://www.aixm.aero/gallery/content/public/AIXM51/AIXM_Feature_Identification_and_Reference-1.0.pdf#page=7
Update README.md
Merge pull request #1 from m-click/fix-xlink-typos

Fix typos in XLink references.
Merge pull request #2 from m-click/fix-broken-xlinks

Fix broken XLink references

We will discuss later what is the best approach - only abstract references? only internal references? For the moment, it's good to fix the broken ones.
Merge pull request #3 from m-click/fix-missing-identifier

Fix missing gml:identifier in a VerticalStructure
Merge pull request #5 from m-click/remove-sequencenumber-from-snapshot

Remove sequenceNumber from SNAPSHOT
Merge pull request #7 from m-click/add-uuid-prefix

Add missing "uuid." prefix to gml:id
Improve style of README.md
Merge pull request #9 from m-click/improve-readme-style

Improve style of README.md
Fix UUID mismatch

There were two ways to fix this: Use consistently either UUID "c1bb..."
or UUID "5909...".

From the document it was pretty clear that "c1bb..." is the correct
UUID.  First, this unit is referenced by "c1bb..." at other places.
Second, there is already another feature with UUID "5909...".