cleanup DSDP interface
Introducing coptoy: a toy convex optimization tool

At the moment, just recognises SDP problems in naturals notation
Add checks for LBX, UBX, LBA, UBA, LBG, UBG

backportable
Update nlp_codegen.cpp
automatic documentation update
automatic documentation update
DSDP: printlevel option and removed debug stray printing
optoy: adding eval
Removed more stray printing from DSDP
Moving DSDPCreate to evaluate

This is against the philosophy of casadi, but it is unavoidable without
modifyng DSDP source
automatic documentation update
Closes #792: customIO
Concerning #792: IOScheme - cleanup
Concerning #792: IOScheme - providing asserts
Concerning #792: IOScheme - boilerplate .derivative()