0.2.0

Add native support for key types:

• unsigned integers(u8, u16, u32, u64, u128)
• signed integers(i8, i16, i32, i64, i128)
• usize
• floating point numbers through Float32/Float64 types(to implement Ord for them)

ByteString type now used only for raw byte sequences and not support conversion from numeric types anymore.
Art no more requires keys to be Ord in most cases, Ord required only for scan operation.