Simple and small birdhouse

The original birdhouse was too big for small birds. I scaled it down to
Z:150mm
X:133mm
Y:174mm
The inlet hole is 35mm in diameter.
It now better suits the Zebra Finch, and other similarly sized birds.

- I have modified the holes for hanging to oval.
- Added 8 air vents on the right side.
- A ladder has been added inside for better movement of the birds.