Add support for indexed (and non-indexed) Event fields types that are distinct `ValueType` or `SmallByteArray`. For example,
```nim
type
DistinctAlias = distinct array[32, byte]
MyEvent = object of Event
a {.indexed.}: DistinctAlias
b: DistinctAlias # also allowed for non-indexed fields
## The below funcs generally need to be included for ABI
## encoding/decoding purposes when implementing distinct types.
func toArray(value: DistinctAlias): array[32, byte] =
array[32, byte](value)
func encode*(encoder: var AbiEncoder, value: DistinctAlias) =
encoder.write(value.toArray)
func decode*(decoder: var AbiDecoder,
T: type DistinctAlias): ?!T =
let d = ?decoder.read(type array[32, byte])
success DistinctAlias(d)
```
Ben Bierens
Mark Spanbroek
Eric Mastro