Update TCPDF to 6.0.037

6.0.037 (2013-09-30)
	- Method getAllSpotColors() was added to return all spot colors.
	- Method colorRegistrationBar() was extended to automatically print all spot colors and support individual spot colors.
	- The method registrationMarkCMYK() was added to print a registration mark for CMYK colors.
	- A bug related to page groups was fixed.
	- Gradient() method now supports CMYK equivalents of spot colors.
	- Example n. 56 was updated.