Include custom headers in model.cpp

[denisalevi]

Fix for issue #131. I only included headers defined via prefs.codegen.cpp.headers.

[mstimberg]

Thanks for the PR! I'm happy with the change in general, but for consistency with the other templates maybe rather use:

{% for name in user_headers | sort %}
#include {{name}}
{% endfor %}

? I don't think we need to support two types of syntaxes to specify headers here.
Also, maybe use user_headers = self.headers + prefs['codegen.cpp.headers'] as in the other places? I am not quite sure why we use self.headers elsewhere (it is an empty list anyway), but it might come in handy some day I guess.

[mstimberg]

Oops, sorry... I just saw that the code I mentioned is used in brian2, not in brian2genn...

[mstimberg]

In the long-term we should make Brian2 and Brian2GeNN consistent with respect to the header syntax, but that's independent of this PR. Happy to merge things.

[mstimberg]

Oh, but note that brian2genn does not work (yet) with brian2 master, due to the changes in the synapse generator.

[denisalevi]

Thanks for the quick merge and the hint! I will stick with the latest brian2 release for the benchmarks.