elixirc should have a --silent option

[alexrp]

It is arguably a bit odd that elixirc outputs anything at all when there are no errors, as most other compilers don't behave this way. It would at least be good to have a --silent option that makes it only output warnings and errors (no Compiled foo.ex and the like).

[ericmj]

I think elixirc should be quiet by default unless given the --verbose option and mix should be verbose by default unless given the --quiet option. Wdyt?

[alexrp]

That works too.

[josevalim]

Agreed with @ericmj. Let's make elixirc not print anything unless --verbose is given.

[pminten]

Working on this.