add "silent" argument to comileNimble()

[danielturek]

Request we add an argument silent to compileNimble(), with default FALSE.

When silent = TRUE, this would suppress all compiler messages. In particular, this would suppress the output:

compiling... this may take a minute. Use 'showCompilerOutput = TRUE' to see C++ compiler details.
compilation finished.

[fritzo]

Hmm, maybe it would should switch to a compilerVerbosity option with three values (and later maybe more values):

• 0 means absolutely no output
• 1 (default) means a little output
• 2 is equivalent to our current nimbleOptions(showCompilerOutput = TRUE)
• 3 might additionally add nimbleOptions(verboseErrors) or something

[danielturek]

Sounds reasonable to me.

[perrydv]

I would add to this that the nimbleModel output is, I think, more disorienting for users and hence would be nice to control / suppress. In particular the list of uninitialized variables can be really ugly.