Create timestamp columns with millisecond precision on MySQL 5.6 and newer

[ricardograca]

This changes the timestamp() and timestamps() schema building methods to output columns that have millisecond precision on MySQL versions 5.6 and newer.

This feature is not enabled by default for now and requires passing a version: '5.6' option when initializing the client to enable. The version number should be your actual MySQL server version, although as long as it is 5.6 or greater the feature will be enabled. The version number can be in the form 5.6 or 5.6.10.

Fixes #2524.

Associated documentation update: knex/documentation#99

[ricardograca]

@elhigu This is still missing the deprecation warning. Any tips on where I should place it? It's also missing documentation but I guess that goes in the documentation repo.

[ricardograca]

No idea why the tests are failing on Node 6 and 8. On Node 6 it seems there's a segmentation fault right after the mocha tests. On 8 an assertion related to migrations is failing. I don't think this is caused by the changes in this PR.

[elhigu]

8 failed to some random fail of oracle tests that fails every now and then. That segmentation fault was strange... I just reran those failing builds.

Yes, docs go to other repo and deprecation message inside that supportsPreciseTimestamps function if client.version is not given. Warning should explain that on older mysql versions they need to pass version: '5.5' or something like that or in future that code will break and with newer ones they need to choose 5.5 or older to keep timestamp precision bad. Maybe linking to documentation would be easieast to prevent having that huge warning message.

[ricardograca]

@elhigu Updated. I also increased the precision to microsecond since this should help reduce rounding errors and I see no reason not to use the highest available precision.

[elhigu]

I just realised that actually every mysql user needs to set that variable to get rid of the warning 😬 So I think the way to go there is to change a error message a bit to be like:

'To get rid of this warning one should specify mysql dialect flavor in the knex configuration. Currently flavor defaults to 5.5, but in future releases it will default to 5.7 that supports high precision timestamps. See http://knexjs.org/#Schema-timestamps for more information."

And then just remove the warning in some future release and change the default.

[ricardograca]

Ok, will do.

[ricardograca]

Updated.

[elhigu]

Thanks a lot!