Usability improvement: cluster overwrite warning

[fredfrance-oss]

It would be nice if there was a warning/error when re-using an existing clustering folder, as it will in the current version always have the risk of placing a new cluster in the existing cl1 folder for example. A stupid demonstration of this is

casr-cluster -c dedups clusters
casr-cluster -c clusters/cl5/ clusters

Which will make cl1 contain both clusters cl1 and cl5.

EDIT:
Previous version of this request asked for stable cluster naming, but this is possible using the casr-cluster -u feature

[SweetVishnya]

We don't have much time to code for this project nowadays. So, pull requests a very much welcomed ;)

[SweetVishnya]

Btw, I don't think that stable cluster number is possible for hierarchical clustering algorithm. As far as I remember, we added determinism as much as possible. If you see more code locations to improve, feel free to suggest changes.

[SweetVishnya]

EDIT:
Previous version of this request asked for stable cluster naming, but this is possible using the casr-cluster -u feature

Oh, I see. So, we really much appreciate pull requests from you that add necessary additional warnings to casr-cluster.