* change TSEncoding.GORILLA to TSEncoding.GORILLA_V1

* add the implementation framework for GORILLA_V2

* support encoding INT32 using GORILLA_V2 encoder

* add the encoders of GORILLA_V2

* add the decoders of GORILLA_V2

* fix tests

* fix tests

* add copyright info in LICENSE

* add copyright info in modified files

* fix bugs and add ITs

* add IT

* update Gorilla encoding user doc

* fix code smells

* change the return type of the method readNextClearBit to byte

* rename default Gorilla encoding to GORILLA