Add changelog entry for 0.6.0

Fix #21

Bump version to 0.4.1

Bump version to 0.4.0

Bump version to 0.3.2

Bump version to 0.3.1

Update to the latest Proximity SDKs [breaking changes!]

- Proximity Zones are now defined by tags instead of attachments

- enter/exit/change actions now receive Proximity Context, which is:
  - the triggering zone's tag
  - the identifier of the beacon that triggered the action
  - the attachments assigned to that beacon

Read more in the iOS and Android SDKs' changelogs:

iOS:
https://github.com/Estimote/iOS-Proximity-SDK/blob/master/CHANGELOG.md#0140---2018-06-19

Android:
https://github.com/Estimote/Android-Proximity-SDK/blob/master/CHANGELOG.md#060-june-18-2018

Bump version to 0.2.0

This enables background support on Android via a notification.

Bump version to 0.1.2

This it to publish the updated README to npm

Bump to v0.1.1