Improve event store indexes

[prolic]

resolves #43

/cc @basz @oqq

[coveralls]

Coverage remained the same at 99.096% when pulling 6c9fee8 on indexes into 1684868 on master.

[oqq]

Some thoughts here: #43 (comment)

[prolic]

See also discussion here: #43 - I added some additional comments there.

[prolic]

PostgresSimpleStreamStrategy is updated to have another indexing including no - same optimization was not successful for MySQL at the moment.

[coveralls]

Coverage increased (+0.002%) to 99.098% when pulling 0d83f0a on indexes into 1684868 on master.

[prolic]

@oqq that should do the trick

@codeliner please review as well - I added a new interface - please check naming and namespace location.

[coveralls]

Coverage increased (+0.002%) to 99.098% when pulling da1ebfa on indexes into 1684868 on master.

[prolic]

need to fix some tests, wait a minute ....

[prolic]

ok ready @codeliner @oqq @basz

[coveralls]

Coverage increased (+0.002%) to 99.098% when pulling 0128e49 on indexes into 1684868 on master.

[codeliner]

LGTM but I 'm not a RDBMS expert. @oqq and @basz please also take a look

[basz]

Looks like a dramatic improvement. Performance is stable at about ~90 commands per seconds (yielding ~3 events each)

    "prooph/pdo-event-store":                           "dev-master as 1.0.0-beta4",

First 180 seconds 92.5 commands/s
Last 180 seconds 88.6 commands/s
done in ~6 minutes

    "prooph/pdo-event-store":                           "dev-master#16848680e2f963fbaf2cdf015c6b788156fe8385 as 1.0.0-beta4",

First 60 seconds 43.6 commands/s
First 180 seconds 38.3 commands/s
Last 180 seconds 9.4 commands/s
done in ~35 minutes

So, thanks for the great work on this @oqq @prolic