* Set BIGDL_IMPORT_IPEX default to true, i.e., auto import IPEX for XPU.
* Remove import intel_extension_for_pytorch as ipex from GPU example.
* Add support for bigdl-core-xe-21.
* add cpu and gpu examples of flan-t5
* address yuwen's comments
* Add explanation why we add modules to not convert
* Refine prompt and add a translation example
* Add a empty line at the end of files
* add examples of flan-t5 using optimize_mdoel api
* address bin's comments
* address binbin's comments
* add flan-t5 in readme