[SIG-13647] allow idents for limits and offsets (#3)

Added Unpivot. Fixed some Pivot (#2)

-- Technically, unpivot has some stricter
   expr requirements (eg instead of expr for ident in col_list
   it should be <column> for ident in col_list). I haven't been
   able to navigate to find this stricter definition yet, but
   maybe we want this fix ASAP.

(cargo-release) sqlparser version 0.9.0

(cargo-release) sqlparser version 0.8.0

(cargo-release) sqlparser version 0.7.0

(cargo-release) sqlparser version 0.6.2

snowflake: ignore/respect nulls for window funcs

Merge pull request apache#263 from ballista-compute/documentation/car…

…go-release-config

add a note about cargo release config

Merge pull request apache#263 from ballista-compute/documentation/car…

…go-release-config

add a note about cargo release config

(cargo-release) sqlparser version 0.5.1