lib/lingo/attendee.rb: Warn about invalid options.

Related to #1.
lib/lingo/attendee/vector_filter.rb: Support `Token`s in addition to `Word`s.
lib/lingo/attendee/{debugger,vector_filter}.rb: Moved debug filter.
lib/lingo.rb (deprecate): Removed method.
{lib,test}/: Hide/remove out-of-date documentation.
.travis.yml: Workaround for rubygems/rubygems#1009.