Use case 1.i: Create and serialise empty model to XML

[codecurve]

From https://github.com/cellml/libcellml/blob/master/docs/usecases.rst:

"Create: Create an [empty] model from scratch and serialise it to XML (the test is that the serialised model matches manually validated XML documents)"

[codecurve]

cellml/libcellml#32 is a subtask of this issue. Since more than one pull request will be made for this issue, I'll only close this issue when the next pull request is made.

[nickerso]

Is there any meaning to use of '[empty]' ? the use case is to create an empty model from scratch. Also, including CodeSynthesis is a separate issue, isn't it?

[codecurve]

The plan is to use CodeSynthesis for XML serialisation and deserialisation via bindings.
I was quoting from the doc, hence the square brackets.

[codecurve]

I've asked @agarny to review pull request #49 for me.
Note that the fail on Linux is due to the need for the Linux BuildBot's cmake to be upgraded to v3.2, @hsorby will do this.
I'm not sure why it is failing on the Windows BuildBot, but a clean checkout and build works fine on my Windows box.