Changes since v0.3:

* NEW FEATURES:
  - Add an option to detect the user movement automatically and
"enter" and "leave" the bus without explicit interaction;

* BUG FIXES:
  - Fixed a bug where a bus which doesn't exist could not
be tracked ("400 Bad Request" on POST /bus);
  - Fixed a bug where the location markers on Google Map weren't being
removed at each new data;

* OTHER CHANGES:
  - Minimum Android version is now Marshmallow (API 24);
  - Updated Gradle dependencies;
  - Minor changes;