Enable defining new functions after agent creation (#285)

* Enable defining new functions after agent creation

* Add notebook for function inception example

* format

* 1. fix bug 2. support remove function

* 1. fix bug 2. support remove function

* 1. add example doc 2. change test file 3. change ipynb title

* Update website/docs/Examples.md

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Co-authored-by: Li Jiang <bnujli@gmail.com>
Co-authored-by: “skzhang1” <“shaokunzhang529@gmail.com”>
Co-authored-by: Shaokun Zhang <shaokunzhang529@gmail.com>
Co-authored-by: Qingyun Wu <qingyun.wu@psu.edu>