Use TMxpElement as a value class to avoid memory leaks.
Merge branch 'release_31' into development

Use TMxpElement as a value class to avoid memory leaks.
Move .clang-format to src directory.

Less unnecessary files in the top directory.
Merge pull request #116 from ahmedcharles/clang_format

Move .clang-format to src directory.
Add new clang-format for new code.
models