Move away from Base.write(::IO, ::POMDP)

[zsunberg]

I don't think specializing Base.write for POMDP is the correct way to implement the functionality in this package.

The docstring for write says "Write the canonical binary representation of a value to the given I/O stream or file." I don't think the pomdp file format is the canonical binary representation they are thinking of based on the rest of that documentation (it talks about endianness). Base.print may be more appropriate, but still probably not what we want.

I think we should look at how DataFrames are written to csv files or how excel files are read in for some inspiration. Or maybe if there is a package that saves neural networks to bson?