Check relation of zres and tolerance

[jirik]

It seems to me that ZRES in case of tolerance does not work as expected. Maybe I have just bad expectations.

I expect that ZRES returns size of 1 pixel for given zoom level. If I set tolerance to this ZRES value I expect that I presicion of geometry is equal to this tolerance. However visually it does not seem to be true. I had to change tolerance for water and transportation because precision was poor: #257 https://github.com/openmaptiles/openmaptiles/commit/555825486ffc3e8c0d103a0f205f550604009b6c

I will look at it later. Maybe it has something to do with the fact that our zoom levels are shifted by one comparing to e.g. Google Maps.

[ghost]

I will look into this too as it was my commit.