RFC: Stopgap nonlinear printing

[joehuchette]

For #201: until we can unravel nonlinear expressions for printing, this just states that nonlinear constraints/objectives exist:

Max (nonlinear expression)
Subject to
1 nonlinear constraints
μ free
σ ≥ 0

[joehuchette]

I'm not going to add tests or anything because I hope this isn't a permanent solution.

[mlubin]

Do we not currently have any tests for printing nonlinear models? I'd say it's worth adding a simple one.

[joehuchette]

What would we test? I didn't add any new methods, just modified print/show for Model. I guess we could test that these work at all for nonlinear models.

[mlubin]

Just printing a basic nonlinear model, otherwise we don't have coverage for this code.

[joehuchette]

Added.

[coveralls]

Coverage increased (+0.41%) when pulling 64287db on nl_print into 417013a on master.

[joehuchette]

Thanks, coveralls!