Fix creating .npmignore instead of .gitignore.

This is in fact npm bug or feature - each .gitignore, even deeper one,
is changed to .npmignore upon `npm publish`.

Renamed .gitignore to different name and added item to rename.json
so it is still saved as .gitignore.
Merge pull request #13 from amber-smalltalk/npmignore-fix

Fix creating .npmignore instead of .gitignore.