Allow split/parameterized queries with ad hoc queries

[ianhelle]

Currently you have a choice between using built-in queries (or defining your own in YAML) or using exec_query which takes an opaque query string.
The latter is flexibly but you miss out on being able to split the queries and using parameters.

The proposal is to extend exec_query as follows:

• If supplied with kwargs, it will try to use these as parameters and substitute them in
  • we might have issues here because we don't control the type - esp. datetime and list conversion
    • maybe we could just check the type of the parameter and apply the default formatting
    • if the param is a string we could test the param to see if it converts to a date and apply conversion
• if split_by is a parameter AND start and end are supplied it will use those to shard the query
  • if split_by and no start and end - produce a warning
  • if split_by and start - assume end = datetime.utcnow()

Another related thing is to simplify add more full-featured queries dynamically (e.g. with param definitions) - these would be added to the query_provider for the duration of the session, maybe also added to pivot functions.

[ianhelle]

More visible help for queries based on table name - e.g. queries for syslog, queries for specific parameters.
Can we look at ad hoc queries and try to identify built-in queries that match (sort of)? Is this too complex?