Install develop dependencies as well
Stop using lib::core::only and PERL5OPT for now, in favor of simpler PERL5LIB. Re: #82 #70 #60

PERL5LIB isn't perfect since it doesn't eliminate site_perl from @INC
in the child process, which means carton exec could accidentally load
modules from site_perl even when they are not available in the
carton.lock.

We'll address this by either implementing a check-like logic in the
exec (which would add an overhead), or add some additional @INC hooks
in the development, which can detect such errors, a la App::FatPacker