Add support for linked variables in neurongroups, with a syntax similar to Brian1. Closes #189
Allow linking from size 1 groups to groups of arbitrary size.
Allow to initialize arrays directly from an array of values (allows to mark an `ArrayVariable` as read-only, and dispenses with one unnecessary variable in standalone)
Allow linking variables with a given index (either as a string or as an array)
Add an example using the `linked_var` mechanism
[skip CI]
Allow connecting groups of different size if an explicit mapping via the "index" argument is given
Allow linking groups of different sizes with explicit indices, but don't allow linking to linked variables that are already indexed.
Allow indexing into index linked variables, but no longer using linked variables with state variables as an index
Allow accessing constant, read-only variables that have been initialized explicitly (static arrays or aranges) in standalone scripts. This should allow the double indexing from the previous commit to work in standalone scripts as well.
Fix a bug that had been silently introduced in commit c6851d75: `CodeRunner` objects were not automatically added to magic networks.
Raise a NotImplementedError when linking to synaptic variables
Refactor the `Variables.add_reference` call to not expect a `Variable` object but a `Group` and a name
Fix the indexing for subexpressions that refer to linked variables.
Merge pull request #264 from brian-team/linked_variables

Linked variables