Update comments and docstrings (add Raises)

Final changes (docs and README update) before 2.0 release
Closes #97 #121 (closed)

Also a big docstrings update is required for the API docs.

Other changes :

• removed one old corner case for OTB<7.4 in functions.py https://gitlab.orfeo-toolbox.org/nicolasnn/pyotb/-/commit/50a51fd20e9d05b14816c6d520520a2ea58f4983?merge_request_iid=101
• factorize one duplicated function: https://gitlab.orfeo-toolbox.org/nicolasnn/pyotb/-/commit/a21aa4dfbcb7212184c3226652c36d5dc1e2abb7?merge_request_iid=101
• light refac in functions.py but no change to the logic : https://gitlab.orfeo-toolbox.org/nicolasnn/pyotb/-/commit/e670786a81614e0596ba9b722a31f68bd3606b70?merge_request_iid=101
• ensure both list or tuple is are accepted for list parameters value
• add an exception is __set_param in case a list is passed to a non list key 848f4e4a