Small rewrite of section 2.1.1.

Added example figure refs, and strengthen argument for format
versions (particularly arguing that there have been other versions)
Try to clean up wording in section 2.1.1.
Slight rewording in section 2.1.1.

change 'read' to 'appropriately handle' for fits parsers. The point
of versioning is not that we forevermore make the format bulletproof
for readers, but rather that readers can appropriately handle conditions
occuring in the file (e.g. new structures they dont know about can
throw exceptions, be skipped over, warnings emitted, etc) which doesnt
really mean they can read the file.
Mark text with note to find data model definition.

Some have expressed doubts about using Wikipedia as source
for definition of 'data model'. Doubtless there are other
CompSci papers we might reference for this definition?
Clean up maxim refs, remove red comment

We dont need to be exhaustive about referencing the maxim. If
one reference has the maxim a little different, I think its ok
to drop it. 2 papers is enough to get the point across.
Try to clear up data model 'questions' and 'information'

An attempt to make our use of 'information' (metadata and data)
consistent in the file. Additionally, try to clean up para 3 in
section 2.1.2 which defines important questions data models may
answer.
Rewrite of section 2.1.2.

Provide definition of namespace, clear up and provide examples of
namespaces, make use of figure 1 for examples.
Add a paragraph about simulation data and reference to Turk et al 2011