Various SQLAlchemy utilities which are a little specific to be proposed to
main SQLAlchemy distribution.

Currently the following features are supported:

  - insert_from_select(table, select) -- adapted from corresponding SQLAlchemy
    example (all copyrights goes to @zzzeek)

  - upsert_from_select(table, select) -- upsert via insert from select with left
    join on target table

  - upsert(table, **values) -- upsert of values

  - sqltype(name) -- shortcut for defining ad-hoc types
