Simplified the backtick object (it's no longer an object, now)

Example:
	-- executes the #{} block, then executes the 'uname -r' command with 'nil' as argument, which is nothing/undef.
	say `uname -r #{"inside backtick".say; nil}`.chomp

Fixed percedence of 'and' and 'or' in Sidef::Exec;