Implement new mod format

[Crauzer]

New format extension should be .modpkg

• modpkg: reading #23
• Writing
• Builder
• Extraction

[moonshadow565]

There are some things that need to be resolved in current implementation, mainly two things are important:

1. Some way to group files belonging together(same wad)
2. Making sure that ModpkgChunk is fixed size

See my review for more details: #22 (review)

[Crauzer]

Tracking in #24