Reorganize the code of benchmark

[presidento]

Decouple the common steps and database implementations. With this it is easy to add new implementations and remove missing ones.

Also separate single writes and batch writes, since in almost every implementation the batch write is faster.

Initiate MAX_TIME to stop spending infinite time calculating very slow implementations.

Add combined case: in real world the key/value stores are not used to store the whole database, then read the whole database. In the combined case the same number of writes and reads are calculated for different database sizes.

WiredTiger is missing from PyPi, so I removed that.

Added SQLite WAL mode, since it is much faster even with autocommit than the existing two.

[presidento]

Here is a sample output with max time = 100:

write

items	lmdbm	vedis	unqlite	rocksdict	dbm.gnu	semidbm	pysos	dbm.dumb	sqlite-wal	sqlite-autocommit	sqlite-batch	dummypickle	dummyjson
10	0.015	0.000	0.000	0.031	-	0	0	0	0.015	0.015	0	0.015	0
100	0.141	0.000	0.000	0.047	-	0	0	0.031	0.031	0.109	0.094	0.156	0.172
1000	1.609	0.000	0.016	0.062	-	0.016	0.031	0.328	0.328	1.015	0.937	1.781	4.250
10000	15.359	0.062	0.062	0.172	-	0.140	0.250	3.219	3.125	- 17.922	19.453	95.188	-
100000	-	0.719	0.672	1.390	-	1.562	2.687	-	31.172	-	-	-	-
1000000	-	9.234	9.140	16.594	-	17.484	27.390	-	-	-	-	-	-

batch

items	lmdbm	vedis	unqlite	rocksdict	dbm.gnu	semidbm	pysos	dbm.dumb	sqlite-wal	sqlite-autocommit	sqlite-batch	dummypickle	dummyjson
10	0.000	0.000	0.000	-	-	-	-	0	0.016	0	0	0	0
100	0.000	0.000	0.000	-	-	-	-	0.032	0.031	0.078	0	0	0
1000	0.000	0.015	0.000	-	-	-	-	0.312	0.109	0.719	0.109	0	0
10000	0.031	0.047	0.046	-	-	-	-	3.140	1.046	- 16.156	1.047	0	0.047
100000	0.422	0.609	0.594	-	-	-	-	-	10.875	-	10.985	0.375	2.859
1000000	4.188	8.500	8.406	-	-	-	-	-	-	-	-	41.760	-

read

items	lmdbm	vedis	unqlite	rocksdict	dbm.gnu	semidbm	pysos	dbm.dumb	sqlite-wal	sqlite-autocommit	sqlite-batch	dummypickle	dummyjson
10	0.000	0.000	0.000	0.031	-	0	0	0	0	0	0	0	0
100	0.000	0.000	0.000	0.031	-	0	0	0	0.031	0.016	0.031	0	0
1000	0.000	0.000	0.000	0.046	-	0.015	0	0.078	0.218	0.297	0.282	0	0
10000	0.047	0.047	0.047	0.093	-	0.109	0.141	0.765	2.079	2.890	3.013	0.031	0.015
100000	0.610	0.641	0.640	0.735	-	1.422	1.797	-	23.797	-	29.375	0.187	0.218
1000000	6.297	8.609	8.765	20.391	-	15.891	20.485	-	-	-	-	2.141	-

combined

items	lmdbm	vedis	unqlite	rocksdict	dbm.gnu	semidbm	pysos	dbm.dumb	sqlite-wal	sqlite-autocommit	sqlite-batch	dummypickle	dummyjson
10	0.156	0.000	0.015	0.047	-	0	0	0.078	0.235	0.390	0.406	0.156	0.156
100	0.156	0.015	0.000	0.047	-	0.016	0	0.078	0.235	0.390	0.390	0.156	0.203
1000	0.156	0.000	0.000	0.047	-	0.015	0.015	0.094	0.235	0.406	0.390	0.188	0.672
10000	0.156	0.015	0.015	0.047	-	0.015	0.031	0.203	0.234	0.469	0.406	0.594	5.141
100000	0.171	0.000	0.000	0.047	-	0.140	0.250	-	0.266	-	0.484	5.547	49.750
1000000	0.172	0.015	0.016	0.047	-	1.297	2.407	-	-	-	-	90.718	-

[Dobatymo]

Hi, thank you for your contribution. I am a bit busy right now, but I will definitely review them soon! It looks like good restructuring.