json

Merge pull request #1222 from dtolnay/rawvalueassoc

Move RawValue associated constants into same impl block as public functions

Merge pull request #1221 from bheylin/add-const-raw-values-for-null-and-bools

Add `'static` lifetime to `const`'s

Add literal 'null', 'true' and 'false' consts to `RawValue` struct.