Crate triomphe

Fork of Arc. This has the following advantages over std::sync::Arc:

• triomphe::Arc doesn't support weak references: we save space by excluding the weak reference count, and we don't do extra read-modify-update operations to handle the possibility of weak references.
• triomphe::UniqueArc allows one to construct a temporarily-mutable Arc which can be converted to a regular triomphe::Arc later
• triomphe::OffsetArc can be used transparently from C++ code and is compatible with (and can be converted to/from) triomphe::Arc
• triomphe::ArcBorrow is functionally similar to &triomphe::Arc<T>, however in memory it's simply &T. This makes it more flexible for FFI; the source of the borrow need not be an Arc pinned on the stack (and can instead be a pointer from C++, or an OffsetArc). Additionally, this helps avoid pointer-chasing.
• triomphe::Arc has can be constructed for dynamically-sized types via from_header_and_iter
• triomphe::ThinArc provides thin-pointer Arcs to dynamically sized types
• triomphe::ArcUnion is union of two triomphe:Arcs which fits inside one word of memory

Structs

Arc	An atomically reference counted shared pointer
ArcBorrow	A "borrowed Arc". This is a pointer to a T that is known to have been allocated within an Arc.
ArcUnion	A tagged union that can represent Arc<A> or Arc<B> while only consuming a single word. The type is also NonNull, and thus can be stored in an Option without increasing size.
HeaderSlice	Structure to allow Arc-managing some fixed-sized data and a variably-sized slice in a single allocation.
HeaderWithLength	Header data with an inline length. Consumers that use HeaderWithLength as the Header type in HeaderSlice can take advantage of ThinArc.
OffsetArc	An Arc, except it holds a pointer to the T instead of to the entire ArcInner. This struct is FFI-compatible.
ThinArc	A "thin" Arc containing dynamically sized data
UniqueArc	An Arc that is known to be uniquely owned

Enums

ArcUnionBorrow

This represents a borrow of an ArcUnion.