Add new command 'dwarf types' to export DWARF info as json

[Pwootage]

This is handy for practice mod and primewatch - it allows me to extract the offsets directly without having to parse the output of the existing 'dwarf dump' command.

The general structure is roughly:

{
  "structs":   [...],
  "unions":    [...],
  "enums":     [...],
  "conflicts": [...]
} 

Each definition contains the size and name, and list of members/values.

Conflicts is a list of structs which the script with definitions that conflict across different compile units.

With Metroid Prime decomp's 0-00, it produces about 4.6mb of json:

 INFO 1496 structs, 10 unions, 384 enums, 40 conflicts