Fixed CMap and SimpleFont parsing

CMap changes
* fixed bug in CMap parsing mentioned in issue #56
* removed unused code
* added some release calls to dealloc

FontDescriptor changes
* do not dump font data into file (probably some forgotten debug)

Scanner changes
* do not convert pdf string with font in StringDetector
* properly create content string
* there is only one possible selection (no need for an array imho)

SimpleFont
* do not treat text as utf8 but as sequence of bytes in simple fonts (as per PDF specification)
* fixed widthOfSpace method (space may also be mapped to some other glyph)

also in readme I fixed example code