32 bit not working

[visr]

First off, great package! I just tried switching GeoJSON.jl over to this use package (PR). But I noticed AppVeyor 32 bit failed with bitcast: argument size does not match size of target type.

I see there is an appveyor.yml, but the service doesn't seem like it is turned on. It would help to catch 32 bit errors. In this case this line fails:

JSON3.jl/src/utils.jl

Line 71 in 37ab02e

string(len) = STRING | Core.bitcast(UInt64, len)

Since len is an Int i.e. Int32 on 32 bit, which refuses to cast to 64 bits.
The Int comes from here:

JSON3.jl/src/read.jl

Line 195 in 37ab02e

@inbounds tape[tapeidx] = string(keylen)