zstd: Add bigger default blocks

[klauspost]

Keep 64K blocks for fastest, but do max size for others.

Healthy compression increase for streams.

(ignore speed)

BEFORE:
github-june-2days-2019.json	zskp	1	6273951764	698989536	12717	470.49
github-june-2days-2019.json	zskp	2	6273951764	617881763	18084	330.86
github-june-2days-2019.json	zskp	3	6273951764	524340691	37059	161.45
github-june-2days-2019.json	zskp	4	6273951764	468052601	170093	35.18
AFTER:
github-june-2days-2019.json	zskp	1	6273951764	698768123	10316	580.00
github-june-2days-2019.json	zskp	2	6273951764	610876538	13942	429.13
github-june-2days-2019.json	zskp	3	6273951764	517662858	42937	139.35
github-june-2days-2019.json	zskp	4	6273951764	464617114	165806	36.09


BEFORE:
github-ranks-backup.bin	zskp	1	1862623243	454073018	4646	382.27
github-ranks-backup.bin	zskp	2	1862623243	418391187	7415	239.54
github-ranks-backup.bin	zskp	3	1862623243	409783212	22014	80.69
github-ranks-backup.bin	zskp	4	1862623243	383832658	124277	14.29
AFTER:
github-ranks-backup.bin	zskp	1	1862623243	454018498	4601	386.01
github-ranks-backup.bin	zskp	2	1862623243	417923331	9886	179.68
github-ranks-backup.bin	zskp	3	1862623243	409613246	24883	71.39
github-ranks-backup.bin	zskp	4	1862623243	383667998	126586	14.03

BEFORE:
nyc-taxi-data-10M.csv	zskp	1	3325605752	641401195	9706	326.73
nyc-taxi-data-10M.csv	zskp	2	3325605752	591748091	14125	224.53
nyc-taxi-data-10M.csv	zskp	3	3325605752	530289687	33988	93.31
nyc-taxi-data-10M.csv	zskp	4	3325605752	476000605	151369	20.95
AFTER:
nyc-taxi-data-10M.csv	zskp	1	3325605752	641305324	10939	289.91
nyc-taxi-data-10M.csv	zskp	2	3325605752	588976126	14511	218.56
nyc-taxi-data-10M.csv	zskp	3	3325605752	529329260	34664	91.49
nyc-taxi-data-10M.csv	zskp	4	3325605752	474949772	143660	22.08

BEFORE:
gob-stream	zskp	1	1911399616	234966570	3484	523.19
gob-stream	zskp	2	1911399616	205669791	4346	419.36
gob-stream	zskp	3	1911399616	175034659	12428	146.67
gob-stream	zskp	4	1911399616	163364634	50935	35.79
AFTER:
gob-stream	zskp	1	1911399616	234891609	3000	607.42
gob-stream	zskp	2	1911399616	203997694	5981	304.73
gob-stream	zskp	3	1911399616	173526523	12201	149.40
gob-stream	zskp	4	1911399616	162195235	49116	37.11