`safePath`/`safeName` utils

[Akryum]

An utility exposed by pathe could help make sure the generated paths are valid under Windows.

See histoire-dev/histoire#256

[pi0]

Path utils cannot silently rewrite paths but we can make a warning when trying to normalize and get such input. (With an internal utils isValidPath)

For the purpose of linked issue and generating a safe name, we can have a new safePath/safeName exports from pathe/utils that does this by replacing illegal chars with path safely (Similar to knitwork.genSafeVariableName it could replace histoire-dev/histoire@69c41c5)

• Note: We could use percent-encoding for this utility. This seems standard Unix<>Windows behavior for fs limitations