Unquote templates, add a warning instead.

[ferd]

Now we get this:

$ rebar3 new lib mylib
===> File "mylib/src/mylib.erl" already exists
===> File "mylib/src/mylib.app.src" already exists
===> File "mylib/rebar.config" already exists
===> File "mylib/.gitignore" already exists
===> File "mylib/LICENSE" already exists
===> File "mylib/README.md" already exists

$ rebar3 new lib my-lib
===> The 'name' variable is often associated with Erlang
module names and/or file names. The value submitted (my-lib)
isn't an unquoted Erlang atom. Templates generated may
contain errors.
===> Writing my-lib/src/my-lib.erl
===> Writing my-lib/src/my-lib.app.src
===> Writing my-lib/rebar.config
===> Writing my-lib/.gitignore
===> Writing my-lib/LICENSE
===> Writing my-lib/README.md

Would resolve #997

[tsloughter]

Great! And nice way way of checking the atom, I was going to do a stupid regex that checked it for certain characters like -, haha, this is way smarter.

[ferd]

Yeah, I started with the regex and got annoyed. Found this in io_lib, works well.

[ferd]

agh let me remove the ?ERROR thing