Type lowering and map[string]ArbitraryType

[philhofer]

Identifier resolution is a pain in the butt.

In any case, the following is now supported

type MyInt int
type Thing struct {
    Which map[string]MyInt `msg:"which_counts"`
}

At the moment we only do lowering for "base" built-ins (int, float64, string, and, as a special case, []byte. Maps and slices are unsupported.) Custom composite types (like type MyFloats []float64) are not yet supported.

Also, there's a bug fix for reading pointers ahead.

[philhofer]

Improves #2 and fixes #3

[philhofer]

As a bonus, c7d5839 has the groundwork for #9.