chore: drop the core to 0.1.0 and restate the stability promise

The API has one set of consumers and no outside users, so declaring 1.0.0
with a stability guarantee was premature. Until 1.0.0 any minor bump may
reshape the API; the written guarantee starts there. Plugins pin 0.1.0.

examples/nemoRepoLastCommit.py

@@ -38,7 +38,7 @@ from gi.repository import GObject, Nemo
 from nemoRepoCore import (findRepoRoot, localDirectoryPath, repoCache,
                           requireCore)
 
-requireCore("1.0.0")
+requireCore("0.1.0")
 
 
 class LastCommitColumnProvider(GObject.GObject, Nemo.ColumnProvider,