add Clone to EventSubscription

[ancazamfir]

As per title, need to be able to clone this.

• Referenced an issue explaining the need for the change
• Updated all relevant documentation in docs
• Updated all code comments where relevant
• Wrote tests
• Updated CHANGES.md

[liamsi]

Thanks!

[codecov-commenter]

Codecov Report

Merging #315 into master will decrease coverage by 0.1%.
The diff coverage is 0.0%.

@@           Coverage Diff            @@
##           master    #315     +/-   ##
========================================
- Coverage    30.6%   30.5%   -0.2%     
========================================
  Files         129     127      -2     
  Lines        4869    4581    -288     
  Branches     1546    1416    -130     
========================================
- Hits         1492    1398     -94     
+ Misses       2295    2216     -79     
+ Partials     1082     967    -115     

Impacted Files	Coverage Δ
tendermint/src/rpc/event_listener.rs	0.0% <0.0%> (ø)
light-client/src/contracts.rs	63.6% <0.0%> (-36.4%)	⬇️
tendermint/src/serializers/raw_commit_sig.rs	16.6% <0.0%> (-16.7%)	⬇️
light-client/src/components/verifier.rs	58.6% <0.0%> (-12.3%)	⬇️
tendermint/src/vote/power.rs	9.0% <0.0%> (-8.4%)	⬇️
light-client/src/components/scheduler.rs	44.0% <0.0%> (-7.5%)	⬇️
light-client/src/predicates.rs	72.7% <0.0%> (-5.2%)	⬇️
light-client/src/operations/commit_validator.rs	40.0% <0.0%> (-3.8%)	⬇️
tendermint/src/validator.rs	43.7% <0.0%> (-3.7%)	⬇️
tendermint/src/serializers/custom.rs	16.6% <0.0%> (-2.7%)	⬇️
... and 65 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 4af6bcb...7895716. Read the comment docs.