Numerapi

- added `burned` to `get_user_activities`
- docs: fixed typos + improved example
- `validation_logloss` -> `validationLogloss`, to follow numerai's docs
- remove everything `originality` related

- added `get_staking_cutoff` to compute staking cutoff for a given round and tournament.
- added `get_nmr_prize_pool` to get the NMR prize pool for a given round and tournament.

- removed `filename` from `get_user_activities`, no longer supported.
- rename `get_submission_filename` to `get_submission_filenames`
- `get_submission_filenames` now only works for the authorized user. It allows
to get ones submission filenames, optionally filtered by round_num and
tournament.

- added `get_rankings`, which gives access to numerai's global leaderboard
- added `get_user_activities`, that allows to see each user's submission and
staking activity
- added `get_submission_filename` to get the submission filename for any user,
tournament & round number combination
- added `prizePoolNmr`, `prizePoolUsd` and number of `participants` to the
`get_competitions` endpoint
- ensure functionality of command line interface is in sync

- added `get_tournaments`
- added `tournament_name2number` and `tournament_number2name` to translate
between tournament numbers and names

- added numerapi command line interface
- allow passing public ID and secret key via environment variables