* Use the TX_TOKEN environment variable to set your Transifex API token.
This essentially replaces the --token argument in the `tx init`
command, and does not write any credentials in the .transifexrc file.
* Add the --no-interactive argument in the `tx pull` command, for the
case where no user input is required. This is needed in some cases
where a CI does not want to proceed with user input and needs to fail
silently.