maps: utility functions to extract keys, values, or both

Extracts from a map keys, values, or both to a properly typed array.
Merge branch 'master' of https://github.com/cookieo9/go-misc into maps

This adds the dbg and flagutil packages.
Updated travis.yml script to manually pull slice package, with full output.
Trying w/o travis.yml hack, using relative import instead.
Update extract_test.go

Cleaned up import juggling.
Update .travis.yml

Cleaned up testing hacks.
Merge branch 'master' of https://github.com/cookieo9/go-misc into maps
Merge branch 'maps' of https://github.com/cookieo9/go-misc into maps
Update README.md

Added maps and sorted subpackages.
Merge pull request #1 from cookieo9/maps

maps: utility functions to extract keys, values, or both