Assembly modding support & objdiff + decomp.me integration

[encounter]

Monolithic PR because this is merging 4 different sets of changes together.

• Assembly modding support
  • Place an .s in asm dir, and it will override the extracted object.
  • Place an .s in src to have it be treated as if it were a matching C file (e.g. for TUs that were originally asm)
• decomp.me support in objdiff (NOTE: won't work until objdiff 1.0.1+)
• Custom REL links handling created for mp4-dtk