Improve the NL writer

[carldlaird]

Improve the performance of the NL writer - several suggestions have been proposed:

1. profile and see if there is low hanging fruit
2. look at implementing a binary NL format
3. look at implementing a C-based writer

Still need to gather data on these options to see which has the most promise.

[whart222]

I think we should call these out as separate activities.

[whart222]

Should we close this?

Option (2) is redundant with #177 .
Option (3) is redundant with #1158

[jsiirola]

Archived on the master Performance Proposals Issue (#1430). Closing this performance proposal until active development has begun.