Add dj.Table.alter() to reduce code duplication in table modification routines
Add parsing and table creation for secondary indexes
Add support for secondary indexes to dj.Table.addIndex and dj.Table.dropIndex. Proposing this as initial implementation for issue #15.
Cleaner implementation of dj.Table.dropIndex for issue #15
Prevent interference of user-defined secondary indexes and foreign key constraints. Table definition syntax without "+++" separator, as proposed in issue #15
Merge branch 'feature/secondary_indexes' of github.com:ahoenselaar/datajoint-matlab into future