Renamed BitmapOffset to GlyphDataOffset
Renamed sbixBitmapSet... to sbixStrike...
Rename sbixBitmapHeader... to sbixGlyphHeader...
Rename self.bitmapSets to self.strikes etc.
Renamed bitmaps to glyphs
Nicer names
Renamed imageFormatTag to graphicType
Rename Bitmap to Glyph
Pad graphicType if len() < 4
Dump sbix flags as a bit field
Use safeEval for attributes
Cleanup
Merge pull request #166 from fontfont/master

sbix: Renamed attributes and classes to stay closer to the spec