Support endless method definition

[schneems]

def square(x) = x * x

irb(main):002:0> Ripper.lex("def square(x) = x * x")
=>
[[[1, 0], :on_kw, "def", FNAME],
 [[1, 3], :on_sp, " ", FNAME],
 [[1, 4], :on_ident, "square", ENDFN],
 [[1, 10], :on_lparen, "(", BEG|LABEL],
 [[1, 11], :on_ident, "x", ARG],
 [[1, 12], :on_rparen, ")", ENDFN],
 [[1, 13], :on_sp, " ", BEG],
 [[1, 14], :on_op, "=", BEG],
 [[1, 15], :on_sp, " ", BEG],
 [[1, 16], :on_ident, "x", END|LABEL],
 [[1, 17], :on_sp, " ", END|LABEL],
 [[1, 18], :on_op, "*", BEG],
 [[1, 19], :on_sp, " ", BEG],
 [[1, 20], :on_ident, "x", END|LABEL]]

Will be interpreted by dead_end as a keyword but not an end:

irb(main):010:0> line = DeadEnd::CodeLine.new(line: "def square(x) = x * x", index: 0)
=>
#<DeadEnd::CodeLine:0x00007fd387985e60
...
irb(main):011:0> line.is_kw?
=> true
irb(main):012:0> line.is_end?
=> false

I think the appropriate thing to do would be to treat this line as both a keyword and an end. However, there might be other logic that wouldn't expect a kw and end on the same line. If we don't