Log Message:
Update to soci 3.2.2:
- Fix uninitialized indicators in conversion_into_type and
  conversion_use_type specialisations
- Fixed placeholder matching for PostgreSQL-style casts with ORM
- Fixed memory leaking in use binding in case of bind/unbind sequence
- Fixed sscanf formatter for MinGW/MSVC in backends
- Fixed partial placeholder name matching for ORM cases
- Added test for use of indicators with rowset<row>
- Added test for get_affected_rows after bulk operations

Add options for selecting MySQL/PostgreSQL/SQLite backends, defaulting
to PostgreSQL.