change gifsicle interlace option to deinterlace by default for better compression, pass `nil` to leave as is
remove app and other extensions from gif images

--no-app-extensions is redundant
analyse variants of same worker running one after another
move all worker initialization to Worker
add specs for worker initialization, move spec for run_order
fix code style in worker_spec
extract worker_double and use instance_double in worker_spec
use init instead of new for initializing workers directly so worker can initialize multiple instances if needed
Merge branch 'worker-init' into better-compress-gif

Conflicts:
	CHANGELOG.markdown
run gifsicle two times: one with interlace off and one with on for best result, resolves #70
changelog entry for gifsicle interlace
fix style (missing comma at end of array)
Merge branch 'worker-init' into better-compress-gif
Merge branch 'better-compress-gif' into bin-checking
shorter code for didn't get version of bin
extract check_fail! from check! in Bin to show warnings only once, resolves #69
add Bin::UnknownVersion error
enhance specs for checking version in BinResolver
rewrite bin checks without nested case statements
Merge branch 'bin-checking' into better-compress-gif