Create RxJava modules

[Mecharyry]

Problem

Merlin has a hard dependency on RxJava1 which forces clients to include it even if not required.

Potential Solution

Modularise Merlin to remove the hard dependency.

Impact

• Clients can choose which packages they require from the Merlin library rather having hard dependencies.
• We can expand to incorporate additional modules for future versions of RxJava.

[Mecharyry]

This has been addressed in #104 and will be released as part of v1.0.0.