### Changes

* Read credentials from the `credentials` key from the SBT plugin ([#257])

This is enabled by default, but isn't fully satisfying as is. `credentials`
is handled by SBT, and seems to acquire a global lock when queried. If a
SBT is starting up elsewhere (initial resolution necessarily not handled by coursier)
or a `publish` command is running in another SBT, these acquire the lock and make the
`credentials` setting, so the update, wait for it. The `coursierUseSbtCredentials` setting
controls whether coursier checks the `credentials` key. It is set to true by
default for now, but may not be so in the future because of this lock issue.

* Disable progress bars by default if the `CI` or `INSIDE_EMACS` environement
variables are set ([#257])

These were already disabled if the current process has no input (that is if
launched with `< /dev/null` - the sbt-extras launcher with the `-batch` option
does that).

By default, Travis CI seems not to provide the `-batch` option to the sbt-extras
launcher, but it does set the `CI` environment variable.

[#257]: https://github.com/alexarchambault/coursier/pull/257

### Non-backward compatible changes

N/A