* lisp/progmodes/ruby-mode.el (ruby-smie-grammar): Improve precedences

* lisp/progmodes/ruby-mode.el (ruby-smie-grammar): Improve precedences
of "and", "or", "&&" and "||".
(ruby-smie--args-separator-p): Prohibit keyword "do" as the first
argument.  Prohibit opening curly brace because it could only be a
block opener in that position.
(ruby-smie--forward-token, ruby-smie--backward-token): Separate
"|" from "&" or "*" going after it.  That can happen in block
arguments.
(ruby-smie--indent-to-stmt): New function, seeks the end of
previous statement or beginning of buffer.
(ruby-smie-rules): Use it.
(ruby-smie-rules): Check if there's a ":" before a curly block
opener candidate; if there is, it's a hash.

* test/indent/ruby.rb: New examples.