Replaced old version of merge_structures.py with the newer
Replaced old version of merge_structures.py with the newer

Before commit b722882c6205950d6113, there were 2 versions of merge_structures.py.
The one in the root directory was the most updated, while the one inside tools
was a version or two behind.

Commit b722882c6205950d6113 removed the updated version in root. In this commit,
the most recent version is restored to its proper location inside tools.

ericchansen/q2mm,arosale4/q2mm,arosale4/q2mm,ericchansen/q2mm,Q2MM/q2mm,Q2MM/q2mm