Update example sound files

Add simple Game Boy startup sound `gameboy-start.blip`. Add new intro to
`test7.blip` and rename to `generic-boss-appears.blip`.
Merge branch 'develop'
Merge branch 'develop'
Merge branch 'develop'
Merge branch 'develop'
Merge branch 'develop'
Merge branch 'develop'
Fix uninitialized variable