Support for maps in parsing as custom stype

Now it properly detects maps as custom types, so e.g. the following will work properly

// GeneratorPrototype is a set of `eqmodel.SensorType` with
// corresponding generator function or value.
//
// The _ID_ is denoting a explicit _ID_, including e.g. ordinal
// and circuit and hence if exist is matched first. If no such
// match, it checks for the base form _ID_. This is just the
// plain _ID_ such as _IDT_. If no match, it checks if there's
// a wildcard match '*' registered. And it will use that.
//
//
// It replaces the _{{ID}}_ in the generator expression so it
// may use the actual _ID_.
//
// .Sample Prototypes
// ====
// 1. IDT_O1: round(generate["IDT_O1"]) - IDT_O1 explicitly
// 2. IDT: round(generate[{{ID}}]) - All IDT matches this one
// 3. *: generate[{{ID}}] - This is last resort, if nothing else matches use this.
// ====
type GeneratorPrototype map[string]string