Serde support for point types

[Boscop]

Please add optional support for serde's Serialize/Deserialize traits.
Like this:

serde = { version = "1.0", features = ["derive"], optional = true }

#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
pub struct Point { // postgis::ewkb::Point

Thanks!

[pka]

What's your opinion about that, @andelf ? I never had a use case for serializing these postgis types since I'm storing them in PostresSQL already, but I still would be open for PR. So I wouldn't activate this feature by default.

[owlot]

I would really like this actually, as we want to be passing PointZ values through grpc and rest requests