* snowflake tests #1687

* actually add the tests!

* merge

* context: #1716 https://github.com/DapperLib/Dapper/issues/1716

- change type-map to allow nullable
- change DateTime/TimeSpan to null
- do not specify DbType for null
- semi-breaking change: swap GetDbType to SetDbType, noting that it is marked [Obsolete] and internal-use-only
- semi-breaking change: make LookupDbType return nullable (same internal-use/[Obsolete])

* add test for Npgsql 6.0.0-rc.1

* try list parameters (like arrays)

* never assign -1 (sentinel) as the .DbType

* postgres tests

Fix verbiage for return type documentation comments.

Another example for "Execute a command Multiple Times" when we have an existing collection. The existing example (which still remains) I found to be a little bit confusing when I had an existing collection. So hopefully this 2nd example will help a tiny bit.

* snowflake tests #1687

* actually add the tests!

Add Documentation for Dapper.SqlBuilder (Issue #688, #480)

This address feedback in #1646

This merges in the work in #1663 and cleans up the convert a bit further.

Fixes #1538 and #1545 by making DbString.ToString() much more descriptive.

Fixes #866. This provides a more informative error, saying _which_ splitOn column couldn't be found in the result set.

Dapper.Contrib is now located at https://github.com/DapperLib/Dapper.Contrib

The used Map method is asynchronous, hence without waiting for operation to complete the benchmark is only counting the query invocation time.

Fix typo in index.md