Pyrates

- added support for complex-valued systems
- added model templates for the kuramoto order parameter and the theta neuron model
- added model templates for the van der pol oscillator and the stuart-landau oscillator
- added support for Python 3.9
- added new example galleries
- extended pytest library
- added the `CircuitTemplate.to_yaml` method that allows to save a given `CircuiTemplate` instance to a YAML definition file
- added the `CircuitTemplate.add_edges_from_matrix` method that allows to connect nodes in a `CircuiTemplate` instance via connectivity matrices
- deleted old, deprecated code fragments
- removed the dependecy on pyparsing

**Full Changelog**: https://github.com/pyrates-neuroscience/PyRates/compare/v0.10.0...v0.10.1

This release presents comes with the following changes:

1. Restructured backend
- new backends (torch, Julia)
- sympy-based equation parsing
- improved compute graph
- improved generation of run functions from compute graphs

2. Improved frontend
- easier imports
- additional convenience functions for simulations
- less steps from model definition to simulation
- reduced syntax for model definitions

3. Removed utility package
- utility packages for parameter optimization, signal analysis and visualization have been removed from the pyrates main package
- most utility functionalities have been moved to separate repositories of the pyrates-neuroscience organization
- less package requirements
- improved structure of the model templates

4. New model templates and documentation examples
- new example galleries and jupyter notebooks with hands-on use examples
- new pre-defined,ready-to-use models

**Full Changelog**: https://github.com/pyrates-neuroscience/PyRates/compare/v.0.9.6...v0.10.0

- Automated translation of edge delays and spreads into systems of differential equations that represent gamma-kernel convolutions does not lead to a mix-up between edges anymore (happened in some special cases previously)
- All zero-weight edges are now removed from the network early during the graph compilation, thus improving compilation time.

v.0.9.6
- `CircuitIR._add_edge_buffer()` was re-worked, such that the algorithm that translates gamma-kernel convolutions for edges into ODE systems is more transparent and computationally less expensive
- additionally improved the source code documentation of `CircuitIR._add_edge_buffer()`
- removed unnecessary copying/indexing operations of original edge source variable

- fixed bugs in the conversion from edge delays and spreads to gamma-kernel convolutions
- ensured that parameters on any network node can be modified via `grid_search`, no matter how that node was defined
- additional consistency, usability and documentation updates

- updated model templates:
- added new QIF model templates with short-term plasticity mechanisms
- improved output variable tracking of Jansen-Rit models
- updates to bifurcation analysis features:
- improved stability and usability of PyAuto
- improved plotting functionalities of PyAuto
- improved automated period doubling cascade continuations
- debugged automatized eigenvalue extraction
- updated parameter optimization and sweep routines