Add support for reading Wii U RPX/RPL

== DETAILS
The Wii U uses a slightly customized ELF format which uses
zlib compression on certain section types.

This commit adds the following:
- add `SHT_` constants for the custom ELF sections
- add `SHF_RPX_DEFLATE` flag used to denote a compressed section
- add code in the section `load()` method to detect the `SHF_RPX_DEFLATE` flag
  and decompress the section