Transparently load state variables from disk in standalone scripts. Closes #177
Adapt monitors to work with the transparent state variable loading introduced in the previous commit.
Adapt tests and examples to the new transparent state variable loading in standalone.
Update the docs for the transparent variable loading in standalone.
Fix for windows
Merge pull request #272 from brian-team/standalone_read_variables

Standalone read variables
Be a bit more careful when linking to index variables and allow some references to pre/post variables to not be available in synapses because of too complicated indexing
Fix an issue surrounding scalar variables and referenced subexpressions. Also explicitly raise a NotImplementedError when trying to use a linked variable with a subexpression -- before it failed with an opaque error message