v0.6

• Fixed bug where moved-from optionals/variants wouldn't destruct their contents
• Fixed bug where emplacing an optional did not destruct the old contents
• Added rvalue reference variant match overload
• Added rpp::launder and used it to guard casts in optional/variant
• Added deduction guides for all container types
• Added handling for volatile qualifiers in reflection infrastructure
• Added slice method to array
• Refactored slice const-ness (now makes use of Slice<const T>)
• Removed slice constructors that took other containers
• Removed redundant movable concept