[close #75] Support endless method definition

[schneems]

When there is an "endless" method definition, we don't want to count it as having a keyword, otherwise when we try to expand it will search for a matching end an possibly introduce a problem in the search.

To detect this case I use the same logic introduced in ruby/irb@826ae90

For reference here are lex of a regular method definition (first line only) and then an "endless" definition:

irb(main):015:0> Ripper.lex("def square(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]]
irb(main):016:0> 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]]

The detection uses a state machine. It knows when it sees an ENDFN state that a function is being defined, but it's not known if it's a "regular" function or not. If the ENDFN is followed by a BEG with a token of = and then a END then it's assumed to be a full "oneliner" AKA "endless" method definition.