Blender Git Loki

Remove the string value from attribute socket.

Attribute sockets should come in varieties for basic data types (float,
vector, etc.) instead of a string. Existing attribute layers should be
accessed explicitly with a "Read Attribute" node (todo).

Typed attributes for basic data will do broadcasting eventually.
This will allow connecting singular value sockets to an attribute input
without the need for a "Fill" node and perform basic broadcasting.