Single ` causes an exception to be thrown

[michele]

If you use a ` in a string, BlueCloth will throw an exception. Example:

irb(main):004:0> BlueCloth.new("In effetti e` un po' cicciotto...").to_html
BlueCloth::FormatError: Bad markdown format near " un po' cicciotto...": No "`" found before end
        from /usr/local/lib/ruby/gems/1.8/gems/BlueCloth-1.0.0/lib/BlueCloth.rb:919:in `transform_code_spans'
        from /usr/local/lib/ruby/gems/1.8/gems/BlueCloth-1.0.0/lib/BlueCloth.rb:264:in `apply_span_transforms'
        from /usr/local/lib/ruby/gems/1.8/gems/BlueCloth-1.0.0/lib/BlueCloth.rb:731:in `form_paragraphs'
        from /usr/local/lib/ruby/gems/1.8/gems/BlueCloth-1.0.0/lib/BlueCloth.rb:723:in `form_paragraphs'
        from /usr/local/lib/ruby/gems/1.8/gems/BlueCloth-1.0.0/lib/BlueCloth.rb:252:in `apply_block_transforms'
        from /usr/local/lib/ruby/gems/1.8/gems/BlueCloth-1.0.0/lib/BlueCloth.rb:204:in `to_html'
        from (irb):4
irb(main):005:0> 

[deveiant]

Thanks for this report. This is basically the same thing as #24, but in a different test case, so I'll keep this as a separate ticket.