Add better support for non-linear equations

Merge pull request #201 from DimitriPlotnikov/master

Make release

Supports PSC models in NEST style

Merge pull request #141 from DimitriPlotnikov/release_0.0.4

Set version to the release version.

First alpha pre-version

Merge pull request #99 from DimitriPlotnikov/master

Optimize symbol table handling. Temporary deactivate a test