Add warning about unused input files
Schema.normalize should no longer create keys for null normalization results. Added schema.format_field. Added StatementSchema.singleton
Restore support for writing normalized input files.
Add schema support to overrides. Fixes #10
Added basic bank account transaction and reconciliation export. Doesn't match previous sorting system, nor does it currently handle statements.
Only output ID column on normalized files if it is actually used.
Add statements to account exports.