Add support for lifetime annotations when using derives

[LegNeato]

Fixes #225

[codecov-io]

Codecov Report

Merging #226 into master will decrease coverage by 0.23%.
The diff coverage is 51.35%.

@@            Coverage Diff             @@
##           master     #226      +/-   ##
==========================================
- Coverage   89.89%   89.65%   -0.24%     
==========================================
  Files          96       96              
  Lines       18167    18311     +144     
==========================================
+ Hits        16331    16417      +86     
- Misses       1836     1894      +58

Impacted Files	Coverage Δ
juniper_codegen/src/derive_object.rs	0% <0%> (ø)	⬆️
juniper_codegen/src/derive_input_object.rs	0% <0%> (ø)	⬆️
juniper_tests/src/codegen/derive_object.rs	89.75% <100%> (+0.56%)	⬆️
juniper_tests/src/codegen/derive_input_object.rs	78.21% <51.51%> (-15.27%)	⬇️

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[djc]

Drive-by review: this looks great! Thanks for fixing my issue. 👍