Add support for BigDecimal with a feature flag

[ambaldwin]

No description provided.

[codecov-io]

Codecov Report

Merging #165 into master will decrease coverage by 0.01%.
The diff coverage is 90.9%.

@@            Coverage Diff            @@
##           master    #165      +/-   ##
=========================================
- Coverage   90.91%   90.9%   -0.02%     
=========================================
  Files          95      96       +1     
  Lines       16288   16313      +25     
=========================================
+ Hits        14808   14829      +21     
- Misses       1480    1484       +4

Impacted Files	Coverage Δ
juniper/src/lib.rs	82.5% <ø> (-2.12%)	⬇️
juniper/src/integrations/bigdecimal.rs	90.9% <90.9%> (ø)

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[theduke]

Hey @ambaldwin21 , thanks for the PR.

I'm afraid I'm sceptical about accepting this.
The other integrations we have are with popular and well-established crates.
BigDecimal is rather young and not widely used.
Accepting it as an integration would mean that we are stuck with it.

For now, if this is something you need often, you could publish a juniper_bigdecimal crate with a wrapper type BigDecimal(::bigdecimal::BigDecimal) that implements the required Juniper traits.

[sporto]

It seems like Diesel has adopted bigdecimal for the numeric PG type.

https://kotiri.com/2018/01/31/postgresql-diesel-rust-types.html

As numeric is widely used and Diesel is very likely to be used with Juniper, maybe this integration should be re considered.

[LegNeato]

Moving discussion to #235