Pass constants as scalars, infer as constants.

[maleadt]

Fixes #78

Interestingly this requires making tfuncs more robust because during initial inference there's now a bunch of UnionAlls (from scalar tile size params being fed into Tuple{} type constructors) that only later get cleaned up by constant propagation.

Depends on maleadt/CompilerCaching.jl#4

[maleadt]

Let's fast-track this since it significantly changes the API.