Warn on note

[jeisch]

I'm using Ngspice version 36

During some simulations, I get messages like these on stderr:
Trying gmin = 1.0000E-05 Warning: Further gmin increment
and
Trying gmin = 3.2781E-05 Note: One successful gmin step

Since neither starts with "Warning:" they are treated as errors, despite the simulation being successful. These modifications allow the "Warning:" to be anywhere in the line to be treated as a warning, and also treats lines that include "Note:" in them as a warning.

[infinitymdm]

This PR is very similar to #313 , though I like how your solution allows keywords to appear anywhere in the line.

That said, shouldn't "Note" be treated as info rather than a warning, as in #313 ? Perhaps you could take some of the ideas they have over there and improve your PR a bit.