Documentation linear algebra functions

[pcchen]

Many linear algebra functions support both "Tensor" and "UniTensor". Currently the documentation for "Tensor" is more complete. For example, Svd_truncate() [1/2] which take "UniTensor" as input, there is no detail information for parameters and returns. We should make both versions to provide the same level of information.

[hunghaoti]

I think some linear algebra function (for example Svd_truncate) support both 'Tensor' and 'UniTensor' is similar and I think we don't need to write two times for it. So I just put the link in 'see also' (UniTensor version will link to Tensor version).