Merge fastCover into DictBuilder (#1274)

* Minor fix

* Run non-optimize FASTCOVER 5 times in benchmark

* Merge fastCover into dictBuilder

* Fix mixed declaration issue

* Add fastcover to symbol.c

* Add fastCover.c and cover.h to build

* Change fastCover.c to fastcover.c

* Update benchmark to run FASTCOVER in dictBuilder

* Undo spliting fastcover_param into cover_param and f

* Remove convert param functions

* Assign f to parameter

* Add zdict.h to Makefile in lib

* Add cover.h to BUCK

* Cast 1 to U64 before shifting

* Remove trimming of zero freq head and tail in selectSegment and rebenchmark

* Remove f as a separate parameter of tryParam

* Read 8 bytes when d is 6

* Add trimming off zero frequency head and tail

* Use best functions from COVER and remove trimming part(which leads to worse compression ratio after previous bugs were fixed)

* Add finalize= argument to FASTCOVER to specify percentage of training samples passed to ZDICT_finalizeDictionary

* Change nbDmer to always read 8 bytes even when d=6

* Add skip=# argument to allow skipping dmers in computeFrequency in FASTCOVER

* Update comments and benchmarking result

* Change default method of ZDICT_trainFromBuffer to ZDICT_optimizeTrainFromBuffer_fastCover

* Add dictType enum and fix bug about passing zParam when converting to coverParam

* Combine finalize and skip into a single parameter

* Update acceleration parameters and benchmark on 3 sample sets

* Change default splitPoint of FASTCOVER to 0.75 and benchmark first 3 sample sets

* Initialize variables outside of for loop in benchmark.c

* Update benchmark result for hg-manifest

* Remove cover.h from install-includes

* Add explanation of f

* Set default compression level for trainFromBuffer to 3

* Add assertion of fastCoverParams in DiB_trainFromFiles

* Add checkTotalCompressedSize function + some minor fixes

* Add test for multithreading fastCovr

* Initialize segmentFreqs in every FASTCOVER_selectSegment and move mutex_unnlock to end of COVER_best_finish

* Free segmentFreqs

* Initialize segmentFreqs before calling FASTCOVER_buildDictionary instead of in FASTCOVER_selectSegment

* Add FASTCOVER_MEMMULT

* Minor fix

* Update benchmarking result