Problems with rendering md file in a subdirectory

Hi Felix,

there is a problem when i render a file in a subdirectory.

    [18:35]-leon@tpad:~/uni/alp4 % themedoc -t default 02/02_uebung.md
    Writing output to 02/02_uebung.pdf
    /home/leon/dev/ruby/themedoc/bin/themedoc:250:in `initialize': No such file or     directory - .02/02_uebung.md.in-header (Errno::ENOENT)
        	from /home/leon/dev/ruby/themedoc/bin/themedoc:250:in `open'
        	from /home/leon/dev/ruby/themedoc/bin/themedoc:250:in `block in <main>'
        	from /home/leon/dev/ruby/themedoc/bin/themedoc:244:in `each'
        	from /home/leon/dev/ruby/themedoc/bin/themedoc:244:in `<main>'


Themedoc tries to creating a temporary file `.02/02_uebung.md.in-header`.
I think it shoud be `02/.02_uebung.md.in-header`.

I also fixed the cleanup, `.resources` didn't get removed. Just added a `-rf`.
Thanks for the tool, I will use it for university stuff.

See you tomorrow, Leon