Partially initialized folder

[fblanchetNaN]

In PR #15 incipyt should be called from an empty/non-existent folder, however it could be a too much restrictive requirement.

Actually this requirement ensures incipyt do not destroy anything, but maybe we can setup a more finer policy.

Let's consider three cases:

• Git: Just skip git init if the folder is already under supervision ? Also skip git add ?
• package folder: Just skip creation of the folder ? What about __init__.py if it doesn't exist ? Create or skip ?
• setup.cfg: What to do ?

A quite easy and general way to do that is setup policy at tool level; three (condition, policy) -- one for each step, pre/add_to/post, policy being skip/fail -- if the condition is met, then the policy is apply. Is any of them is "fail", incipyt stops. Eventually with a superset policy being "do not overwrite any file".

A related question is, what we do if incipyt failed while some files have been written ? Delete or keep them in place ?