Allow replacing nodes with other types

[steveRoll-git]

In some tests, the diagram is modified so that components are replaced with other ones - for example a Shift Left 2 being replaced with a Shift Left 3.

[yontank]

Should be a sub issue of #11
we can do two things that can be helpful:

• some nodes can get an arguement, for example srl will be srlX where x is the number of shifts
• the ability to create a fully customized node given a typescript function

[steveRoll-git]

* some nodes can get an arguement, for example `srl`  will be `srlX` where x is the number of shifts

We're already doing that - we create NodeType objects and they can take parameters

* the ability to create a fully customized node given a typescript function

Maybe at some point in the future but this is too complex for now