Adding shrinking flag for cover and fastcover (#1656)

Adding shrinking flag for cover and fastcover (#1656)

* Changed ERROR(GENERIC) excluding inits

* editing git ignore

* Edited init functions to size_t returns

* moved declarations earlier

* resolved issues with changes to init functions

* fixed style and an error check

* attempting to add tests that might trigger changes

* added && die to cases expecting to fail

* resolved no die on expected failed command

* fixed accel to be incorrect value

* Adding an automated shrinking option

* Fixing build

* finalizing fixes

* fix?

* Removing added comment in cover.h

* Styling fixes

* Merging with fb dev

* removing megic number for default regression

* Requested revisions

* fixing support for fast cover

* fixing casting errors

* parenthesis fix

* fixing some build nits

* resolving travis ci syntax

* might resolve all compilation issues

* removed unused variable

* remodeling the selectDict function

* fixing bad memory access

* fixing error checks

* fixed erroring check in selectDict

* fixing mixed declarations

* modify mixed declaration

* fixing nits and adding test cases

* Adding requested changes + fixed bug for error checking

* switched double comparison from != to <

* fixed declaration typing

* refactoring COVER_best_finish() and changing shrinkDict

* removing the const's

* modifying ZDICT_optimizeTrainFromBuffer_cover functions

* fixing potential bad memcpy

* fixing the error function for dict size