Jitcdde

* Fixing issue 17 due to updates of SymEngine.
* Added quick installation check.
* Improved error messages.

* Added examples for networks and time-dependent delays to documentation.
* Improved error messages.
* Improved addressing of initial discontinuities in fringe cases such as ODEs.

* Added utility function `quadrature` for continuous delays.
* Some improvements of documentation.

* Fixing some under-the-hood inefficiencies.
* Hopefully fixed [this issue](https://github.com/neurophysik/jitcdde/issues/10) with Unicode and Jinja2 on MacOS.
* Some improvements to documentation.

There now is a SymEngine version number to refer to as a dependency – which means that automatically installing this dependency should work and you do not have to build SymEngine on your own anymore.

* Switched from SymPy to SymEngine as a backend, which may speed up code generation by a factor of up to nine hundred. Almost everything that worked before should still work. See [SymPy vs. SymEngine](http://jitcde-common.readthedocs.io/en/latest/#sympy-vs-symengine) for details. As a required [Symengine release is pending](https://github.com/symengine/symengine.py/issues/204), you have to [build it from source](http://jitcde-common.readthedocs.io/en/latest/#building-from-source) for now.
* Added OpenMP support.
* Added variant for transversal Lyapunov exponents.
* Several improvements to documentation.
* Changed some default parameters and behaviours.
* Dropped support of some old, rarely used syntax.
* Dropped Python 2 support.