Git2net

* Added networkx dependency

What's Changed
* Speedup of disambiguate : insertion step by wschuell in https://github.com/gotec/git2net/pull/39
* Report commit hash when processing errors by wschuell in https://github.com/gotec/git2net/pull/36
* Extended pytest setup
* Added option for networkx output to co-editing network
* Switched to logging instead of print outputs

**Full Changelog**: https://github.com/gotec/git2net/compare/1.6.3...1.7.0

* Fixed typo if use_blocks is being used. by cmtg in https://github.com/gotec/git2net/pull/35

* Fixed bug where the mailmap check failed on author names with leading `--`.

* Fixed error message when using git2net with an incompatible version of git.

* Added the module `complexity` allowing to compute various complexity measures before and after all file modifications in commits.
* Added a new tutorial on how to use the `complexity` module.
* Added options for disambiguation and complexity computation to the command line version of `git2net`.

* Removed `extract_complexity` option from functions in the module `extraction`. This functionality is now provided by the new `complexity` module.