New Payload interface that properly maps to only a payload
Added timestamp support into trackers

- Fixes #26
Newline between license and package
Added support for context as maps

- Fixes #11
- Note that we've used the interface Map and not HashMaps in particular to give the option for users
Removed support for context as a string

- Fixes #44
Merge branch 'feature/hashmap-support' into develop
Fix for warnings
Fix for warnings & unused code
Replaced println with SLF4J

- Added some basic logging for trackers when sending events, and HTTP messages being sent.
- Fixes #15
Merge branch 'feature/slf4j' into develop