Make start functions return a Result

[msrd0]

Fixes #483

[codecov]

Codecov Report

Merging #568 (ed9c818) into master (0510afa) will increase coverage by 0.08%.
The diff coverage is 27.58%.

❗ Current head ed9c818 differs from pull request most recent head 805d262. Consider uploading reports for the commit 805d262 to get more accurate results

@@            Coverage Diff             @@
##           master     #568      +/-   ##
==========================================
+ Coverage   85.14%   85.22%   +0.08%     
==========================================
  Files         111      111              
  Lines        5768     5774       +6     
==========================================
+ Hits         4911     4921      +10     
+ Misses        857      853       -4     

Impacted Files	Coverage Δ
examples/cookies/introduction/src/main.rs	88.88% <0.00%> (ø)
examples/diesel/src/main.rs	86.90% <0.00%> (ø)
...les/example_contribution_template/name/src/main.rs	76.19% <0.00%> (ø)
examples/finalizers/src/main.rs	85.71% <0.00%> (ø)
examples/handlers/async_handlers/src/main.rs	91.24% <0.00%> (ø)
examples/handlers/form_urlencoded/src/main.rs	83.33% <0.00%> (ø)
examples/handlers/multipart/src/main.rs	76.19% <0.00%> (ø)
examples/handlers/request_data/src/main.rs	88.88% <0.00%> (ø)
...xamples/handlers/simple_async_handlers/src/main.rs	90.00% <0.00%> (ø)
...s/handlers/simple_async_handlers_await/src/main.rs	90.38% <0.00%> (ø)
... and 29 more

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[FSMaxB]

I'm not entirely sure if it is a good idea to return a std::io::Result here since it doesn't allow for adding additional errors that can be returned. Maybe it's a better idea to introduce an opaque, gotham-specific error type here?

[msrd0]

Good point. Probably some non-exhaustive enum that for now just stores io::Error would be better. Do you want to create a PR?

[FSMaxB]

Do you want to create a PR?

Not really at the moment.