change load path from pop_cap to popcap

change load path from pop_cap to popcap
rename certain internal references from pop_cap to popcap
add memoization & #reload! to AudioFile tag reading methods
update README to document #reload!
add PopCapSpecHelper.benchmark method to show time elapsed for a method call
replace Taggable.tags OpenStruct with internal TagStruct class
update to version 0.6.0
refactor TagStruct into separate class
refactor Taggable to use new TagStruct class
update to version 0.6.1
add MissingDependency error if FFmpeg not installed
refactor AudioFile to use dependency injection for FFmpeg
refactor error raising from Converter class
encode ffprobe raw output as UTF-8 to prevent invalid byte sequence
update rspec
add check for already defined methods on TagStruct
update to version 0.6.5