Add support for the canonical introspection query

[LegNeato]

Fixes #307.

I also fixed all the book tests to run and I am too lazy to put them in a different PR 🤷‍♂️

[codecov-io]

Codecov Report

Merging #337 into master will increase coverage by 0.57%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #337      +/-   ##
==========================================
+ Coverage   87.73%   88.31%   +0.57%     
==========================================
  Files         101      103       +2     
  Lines       14255    14853     +598     
==========================================
+ Hits        12507    13117     +610     
+ Misses       1748     1736      -12

Impacted Files	Coverage Δ
juniper/src/lib.rs	87.09% <100%> (+6.14%)	⬆️
juniper/src/tests/schema_introspection.rs	100% <100%> (ø)
juniper/src/tests/introspection_tests.rs	94.5% <100%> (+0.99%)	⬆️
juniper/src/introspection/mod.rs	100% <100%> (ø)
juniper/src/http/playground.rs	0% <0%> (-25%)	⬇️
juniper/src/http/graphiql.rs	0% <0%> (-20%)	⬇️
juniper/src/schema/model.rs	90.65% <0%> (+3.27%)	⬆️
juniper/src/schema/schema.rs	93.45% <0%> (+6.54%)	⬆️

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[theduke]

👍

LGTM

[theduke]

@LegNeato actually, why do we need the with description / no description split?

[LegNeato]

@theduke I don't know, I just followed what graphqljs did. I would imagine it is probably for space savings?

[LegNeato]

@theduke confirmed with the GraphQL.js team that it to save data/space when the result is read by a machine. If the target is a dev tool that wants descriptions then you include them, but if the target is a code generator that doesn't need them then you can save the download bytes.