v1.6.0

What's Changed

• Support ncurses extended colors API by @shugo in #130
• Add Window#attr_set and Window#attr_get by @shugo in #131
• Do not use wattr_set() if wattr_get() is unavailable by @shugo in #132
• Do not use rb_f_notimplement for attr_set/attr_get by @shugo in #133

Full Changelog: v1.5.4...v1.6.0