Many users seem to stumble over creating new sites in existing non-empty directories. And that `--force` is the necessary option. So I added *See --force* as a hint to the error.
Fixes#4825.
The main item in this commit is showing of errors with a file context when running `hugo server`.
This can be turned off: `hugo server --disableBrowserError` (can also be set in `config.toml`).
But to get there, the error handling in Hugo needed a revision. There are some items left TODO for commits soon to follow, most notable errors in content and config files.
Fixes#5284Fixes#5290
See #5325
See #5324
