Make asm spacing easier to read

Also adds a #prepends callback to Payload::Windows to make it a little
clearer what's happening.
Unstupid the prepends callback

Windows#prepends was overriding PrependMigrate#prepends
Move prependmigrate.rb for naming consistency
Make #prepends() actually work
Merge pull request #3 from jlee-r7/scriptjunkie-migrator

Proposed changes for PrependMigrate