Squashed 'external/geomtk/' content from commit 53ddbdc

git-subtree-dir: external/geomtk
git-subtree-split: 53ddbdcf618080a56b3b2754cdf50b0a2efec83e
Merge commit 'fe4e511ab5fb5618a604ceb90202d232d0d548dd' as 'external/geomtk'
Add initial codes