include markdown copies BOM to output

[Bernhard Weichel]

if you include a markdown fragment, BOM is copied to the output. For example including af file like this

#headline

will have invisible characters in front of # and therefore does not recognize the headline.

possible fix in class.proolib.rb line 162:

 replacetext_raw=File.open($2,:encoding => 'bom|utf-8').read