Update MTPDF.h

Changed header file for new methods
Update MTPDF.m

Created new method to draw in an image context instead of a PDF context.
Update README.md

Added documentation to the new draw methods explaining when and how to use drawInContext:atSize: and drawInPDFContext:
Update MTPDF.h

Added some basic documentation on the new methods to the header file.
Merge pull request #4 from Vortec4800/master

Fixed issue when drawing in UIView context