Outer products
    syntax [DONE]
    typechecking
    IL and codegen

Add M dot v, v dot M, and M dot N

Identity matrix [DONE up to code generation]

trace [DONE]

expand trace in mid to low translation

extend norm (|exp|) to all tensor types

Infix dot product and cross product [DONE]

lerp on scalars and vectors [DONE]

Use ∇⊗ etc syntax
    syntax [DONE]
    typechecking
    IL and codegen

Add sequence types
    syntax
	types: ty '{' INT '}'
	value construction: '{' e1 ',' … ',' en '}'
	indexing: e '{' e '}'

IL support for higher-order tensor values (matrices, etc).
    tensor construction
    tensor indexing and slicing

Add type aliases for color types
    rgb = real{3}
    rgba = real{4}