Error handling

[Billzabob]

Mostly 3 unrelated changes:

• Refactored build.sbt to match what I saw in other open source libs. It doesn't make too much of a difference now but it'll be nice when we add a documentation page.
• Changed error handling so that it fails right away and the stack trace has more info about the failure. For example, now you'll see that Discord reports Invalid shard. in the output because we were sending null for the shard field on Identify (see next bullet).
• Quick temporary fix to the Identify encoder issue involving nulls seen in Discord doesn't treat null JSON fields and absent JSON fields the same #29.

[codecov]

Codecov Report

Merging #35 into master will decrease coverage by 4.87%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master      #35      +/-   ##
==========================================
- Coverage   50.37%   45.50%   -4.88%     
==========================================
  Files          59       59              
  Lines         397      400       +3     
==========================================
- Hits          200      182      -18     
- Misses        197      218      +21     

Impacted Files	Coverage Δ
src/main/scala/dissonance/Discord.scala	0.00% <0.00%> (ø)
src/main/scala/dissonance/Main.scala	0.00% <0.00%> (ø)
...ain/scala/dissonance/model/identify/Identify.scala	0.00% <0.00%> (ø)
src/main/scala/dissonance/model/embed/Field.scala	0.00% <0.00%> (-100.00%)	⬇️
src/main/scala/dissonance/model/embed/Image.scala	0.00% <0.00%> (-100.00%)	⬇️
src/main/scala/dissonance/model/embed/Video.scala	0.00% <0.00%> (-100.00%)	⬇️
src/main/scala/dissonance/model/embed/Author.scala	0.00% <0.00%> (-100.00%)	⬇️
src/main/scala/dissonance/model/embed/Footer.scala	0.00% <0.00%> (-100.00%)	⬇️
...c/main/scala/dissonance/model/embed/Provider.scala	0.00% <0.00%> (-100.00%)	⬇️

---

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 dfeb378...e121624. Read the comment docs.