Declare licenses for all the tools

[Rangi42]

Unlike the disassembly/decomp projects, these tools are wholly original to their authors. Licensing them would be convenient for letting other people use and modify them.

Licenses so far:

• free_space.awk and gbdiff.sh are by Eldred Habert under the MIT license ^^
• png.py is a third-party library under the MIT license
• LodePNG is a third-party library under the zlib license
• All of my own scripts are under the MIT license

What's left:

• unnamed.py (first added by @mid-kid in Add tool to find unnamed symbols: Take 2 pokecrystal#599)
• free_space.py and mapreader.py (first added by @Tauwasser in pret/pokegold-spaceworld@bd9e0d9)
• compare.sh (trivial but nevertheless)

[aaaaaa123456789]

Anything I've written (such as lzcomp) is public domain. If there's no explicit disclaimer, I'll be happy to add one.

[Rangi42]

I've declared all of my code here as MIT.

[Rangi42]

We could just remove compare.sh; gbdiff.sh is more advanced.