removed unused files
renamed variational feature to "variational:order"
support reading/writing ngram counts
added insert/erase and piece-based initialization
simplified kbest computation
added non-const begin() and end()
added diversified cube-pruning and kbests
removed gitignores since they are automatically generated
updated makefile
Merge branch 'master' into diverse
updated from  the latest kenlm
Merge branch 'master' into diverse
implemented sample a kbest like interface to sample derivations
revised sample.sh again
faster sampling when # of edges is only one
bugfix for posterior operation with different feature name
removed frontier flag
bugix for diversified cube prunign and implemented sampling pruning
added help message
Use the interface similar to kbest