Improve option of LOAD api

[asha-ndf]

According to this doc(https://github.com/jupyter-xeus/xeus-sqlite/blob/master/docs/source/api.rst), LOADhas options [R/ RW].
However only [r / rw] can use. This different is just big letter or not.
To edit doc is one of the solution, but I think adding [R / RW] in https://github.com/jupyter-xeus/xeus-sqlite/blob/master/src/xeus_sqlite_interpreter.cpp is the best.

[marimeireles]

Oh! Thanks for reporting this, never really tried, will let you know once I fix.

Or feel free to have a look at it yourself too... If you want, I think the problem is inside the void interpreter::load_db(const std::vector<std::string> tokenized_input) method. We have a few methods in the util.cpp file that can be useful, like to_upper and case_insentive_equals, not sure if the latter would have to be used.

Thanks for the issue! :)

[marimeireles]

The docs were fixed, but this still needs attention.
Thanks again for opening the issue :)