Enable decimal_floats by default for Value::Number(Float) roundtrip

[juntyr]

• I've included my change in CHANGELOG.md

Fixes #337

[juntyr]

?r @torkleyy This PR simply makes decimal_floats on by default
(a) as it fixes #337 as integer floats are now serialized as decimals by default
(b) imo it also looks nicer

[kvark]

Does it even need to be an option?
I would think just removing the option entirely and doing this unconditionally would be better.

[juntyr]

@kvark Does it even need to be an option? I would think just removing the option entirely and doing this unconditionally would be better.

That's a good idea - thanks for the suggestion! This commit will of course require a version bump as it is a breaking change, though I guess the usefulness of not including a decimal was questionable from the start.