Pydriller

New features:
- 'HEAD' can now be used as filter in 'single', 'from_commit' or 'to_commit'
- if the user specify a commit that doesn't exist in a commit filter, Pydriller raises an exception
- GitRepository doesn't contain the function "parse_diff()" anymore. Now it is available in the Modification object


Bug fix:
- 'from_commit' and 'to_commit' are automatically swapped when used with 'reversed_order'

Many updates for this release!

1 - new process metrics: now pydriller can calculate commits count, contributors count, contributors experience, history complexity, hunks count, lines count and minor contributors. Everything in just one line! Thank you stefanodallapalma
2 - fix bug of the filters from_commit and to_commit. In some cases it was returning more commits than it should have
3 - fixed a bug that was causing problems in Windows machines when too many runs were launched contemporary


Deprecated
1. `parse_diff`: now you can find this information directly in the modification object

- we stopped using git hyper blame, and instead we use --ignore-revs (git > 2.23)
- new "clone_repo_to" option to clone the repository in a predefined folder

Thanks to marco-c and jphgoodwin for the PRs.

Thank you to yusufsn, s0nata, stefanodallapalma for the awesome ideas (and/or PRs).

This release includes:
- new filter to skip changes with whitespaces only (see `git diff -w`)
- new algorithm to diff files (see `git diff --histogram`)
- a new class `ProcessMetric`, that can be used to obtain process metrics at file level.
- bug fix on getting the main branch of a detached repository

Small improvements and bugs fix on _git hyper blame_

- removed leftovers prints from git_repository