CHANGES IN crfsuite VERSION 0.4.2

Drop C++11 specification in Makevars
Remove CITATION file
Minor cosmetic changes to remove some Pedantic compiler messages in rcpp_crfsuite.cpp and crfsuite.h
Comment out rumavl_strerror in rumavl.h as the function is not used and in order to avoid 'warning: function declaration isn't a prototype [-Wstrict-prototypes]'
Fix in mem_mgr of ramvl.c caused by update of valgrind 3.21.0 which is now flagging 'realloc with size 0' in packages
Fix memory leak when extracting the hyperparameters from the model with Trainer::params in crfsuite.hpp

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