In particular:
 * use def rather than assigning lambda function
 * unused imports
 * 'X not in Y' vs 'not X in Y'

An example of this is e.g. EUC-TW

In some cases, it seems to find an encoding that's not valid for the
entire string.

* Docker image: Fix ownership issue with Git 2.36+

* Update tests.yml

Add pyproject.toml.

Handle SymrefLoop. Fixes: #293

Support 'main' as a default branch name to try.

Fix InternalServerError when viewing history of a blob.

[ci skip]

This should fix exceptions with undefined newblob, when there's a submodule that's the first path in the tree.

This at least allows rendering pages rather than throwing 500s.

* Actually test blame in blame tests.

* Prepend to PYTHONPATH rather than overriding it.

This is convenient for those of use that e.g. pull in httpauth through
PYTHONPATH.

* Support viewing blame of empty files.

Without this, klaus tries to access repo[b''] which leads to a KeyError.

* Update runtests.sh

Co-authored-by: Jonas Haag <jonas@lophus.org>

Co-authored-by: Jonas Haag <jonas@lophus.org>

Close #250

This allows building forks etc by specifying e.g. a git+http:// URL.
If the argument is not specified, KLAUS_VERSION behaves as before.