Feat/snowflake support and docs

[b-per]

I tested the rest of the features on Snowflake this morning

• a small change was required to make generic_assertions work (` is not a valid object quoting char in Snowflake)
• __not_null__ and __unique__ actually work without any change required, as long as we only use top level fields
  • by personal experience, objects/strucs are less used in Snowflake than in BigQuery so I wouldn't expect most people to want to use nested fields on Snowflake

I also updated the README with the latest info.

Is there anything that you would like me to add be fore making a "non alpha" release with support for Snowflake. I am happy to continue helping here.

[AxelThevenot]

You are a true hero for me you have no idea at which point ! 😂😍

Thank you very much for the fixes in typo, README and for your work, it really helps me because I do it on my free time (and I have not so much of it)

No worry if nested are not supported in helpers, those are only helpers and if someone want this nested assertions it is still possible to create a custom assertion, so everything is fine

The alpha was for you, if you think everything is correct, I made a release 1.1.0 (you can update the README and I will release it)

Thank you so much !

[b-per]

Done, I removed alpha from the README for Snowflake, so it is ready for the 1.1 release whenever you can