Upper case in the name of the Package blocks the generating system

[luisaforozco]

Checklist before submitting a bug report

• I have checked the existing issues and couldn't find an issue about this bug.

Bug details

Describe the bug

I had a previous package named grainLearning and want to apply the template to it. When reaching the second question I am blocked because the name has an upper case L in the name. Github allows to have upper case letters in the name.

To Reproduce

Steps to reproduce the behavior:

1. install copier using :

python3 -m pip install --user pipx
python3 -m pipx ensurepath
pipx install copier

2. run copier copy -r HEAD https://github.com/nlesc/python-template.git ./
3. Select a profile: Let me choose (decide each feature yourself)

Error Message
Package name must start with a letter, followed one or more letter, digits or underscores all lowercase.

Expected behavior

I cannot continue with the process. It should allow to pass if you are really sure of the name.

[sverhoeven]

PEP8 prefers lower case, see https://peps.python.org/pep-0008/#package-and-module-names .
To give the right example we should follow PEP8, and allow uppercase and give a warning.