refs https://github.com/firebaseco/mongoose-attachments/issues/15 : cherry picked https://github.com/joewright/mongoose-attachments/commit/65b4ba6698f0686b5e0f4e241bf94e31b12ccc8f for https://github.com/firebaseco/mongoose-attachments/issues/11
merge from firebaseco master
Merge pull request #17 from nuarhu/versionprep010

Removal of providers and update of README
Version bump to 0.1.0. Updated copyright notice.
Added keywords to package.json to enhance plugin discovery
Added additional keyword into package.json
Added the filenameId attribute.

filenameId allows the user to customize the filename.
Before: /dir/objectId-original.jpg
Now: /dir/<custom-model-attribute>-original.jog
Merge pull request #20 from SeyZ/patch-1

Added the filenameId attribute.