Command traits

[jamiebrynes7]

Following on from @randomPoison's ideas in #121 and examples in various previous PRs, this PR splits out the CommandResponse and CommandRequest traits from the Component trait.

It also restructures the traits somewhat such that there is a Commands trait which is only implemented if there any commands associated with that component. This cuts down on unnecessary generated code and models the domain (schema) a bit more accurately.

There are a number of associated changes in this PR:

• Refactored StatusCode in command response ops to just be a plain old Result<T, E>.
• Removed some unused types/methods
• Moved command related things into the commands.rs file

[codecov[bot]]

Codecov Report

Merging #166 into master will increase coverage by 0.88%. The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #166      +/-   ##
==========================================
+ Coverage   20.10%   20.99%   +0.88%     
==========================================
  Files          41       41              
  Lines        4188     3997     -191     
==========================================
- Hits          842      839       -3     
+ Misses       3346     3158     -188     

Impacted Files	Coverage Δ
project-example/src/generated.rs	0.00% <0.00%> (ø)
project-example/src/main.rs	0.00% <0.00%> (ø)
spatialos-sdk/src/worker/commands.rs	12.76% <0.00%> (-15.81%)	:arrow_down:
spatialos-sdk/src/worker/component.rs	13.04% <ø> (+3.95%)	:arrow_up:
spatialos-sdk/src/worker/connection.rs	0.00% <0.00%> (ø)
spatialos-sdk/src/worker/op.rs	6.22% <0.00%> (+0.10%)	:arrow_up:
spatialos-sdk/src/worker/schema.rs	3.59% <ø> (ø)
spatialos-sdk/src/worker/schema/object.rs	44.68% <0.00%> (-0.98%)	:arrow_down:
spatialos-sdk/src/worker/schema/bundle.rs	86.31% <0.00%> (-0.77%)	:arrow_down:
spatialos-sdk/src/worker/snapshot.rs	79.06% <0.00%> (-0.48%)	:arrow_down:
... and 16 more

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[jamiebrynes7]

Sorry for taking so long to get to this, btw!

Oh no, don't worry about it 😄