Example code in doc disappear

[hunghaoti]

I note that since we have remove the folder 'example' in main repo. That cause some of the example code (for instance:the constructor of the UniTensor) in the api doc generated by doxygen disappear. We may need to add them back which we have used.

[j9263178]

Will add them back in the coming merge.

[hunghaoti]

Logo in documentation disappear (upper left).