Release 2.0.2.0

Improve the compression/decompression rate by 5-20% in the best compression mode.
The compression ratio is improved a little bit than sz 2.0.1.0.
Fix the compilation issue in the previous release (fix the typo in Makefile.am)
Fix the bug in SZ_Init_Params(), which was introduced during the reorganization of parameter structure.
Also revise the testdouble_compress.c to show how to use SZ_Init_Params() function to initialize the environment without reading sz.config.
Revise Makefile.bk so that it includes zstd library and also it's consistent with Z-checker.
Fix a bug in point-wise relative error bounded compression.
Add CMake option to do the compilation.