[POC] Support numbered parameters

[zerg000000]

POC #405

Approach

Change the internal presentation of sql from string to nested vector of sql fragments.
Convert back to SQL string only on public consumer API sql/format, sql/format-expr.

• Replace all (str ...) and (str/join ...) to vector/interpose.
• Replace hardcoded "?" to marker :parameter-marker
• Convert parameter marker to '?' or '$1' when convert sql fragments to string.

Good

• No impact on user that only use helper or format
• Minimum changes in current code base

Bad

• Breaking changes in extension API
• Internal Presentation become a forest of vectors

Checklist

• workable implementation for discussion
• Pass all tests
• Update documentation

Thoughts

• Align all internal/extend fn to output [sqls params], all external fn to output [sql param1 param2 ...] may help to make code even more concise.
• Separate user api/extension api. e.g. format-expr separate into format-expr and -format-expr.
• Standardize the intermediate presentation format.

[seancorfield]

Breaking the representation is not acceptable.