Advanced conversion operations

[sharkdp]

users might also like to explicitly convert to:

• a base SI representation, like kg m³ / s², e.g. expr -> base
• a shortest-possible representation, e.g. J·m e.g. expr -> shortest
• to the canonical representation (see also Canonical unit for dimension #3), e.g. expr -> canonical

Do we also need/want to allow for conversions to dimensions? is something like expr -> Energy useful? Users could always add type annotations, i.e. use sth like expr: Energy to make sure that something is an energy.

see #3 for implicit conversions

[sharkdp]

Maybe we should not use the -> … syntax for this, but rather make use of the postfix apply operator: expr // to_base

[sharkdp]

See also: #116

[sharkdp]

See also: #373 305