Added not null constraints to tables in lib_tables
Merge pull request #16 from g2-aj/g3-ks

Added not null constraints to tables in lib_tables
completed checksOverdue items clerk transaction, and fixed Borrower to calculate an expiry date based on the current date
Merge pull request #17 from g2-aj/branch_alshahna

completed checksOverdue items clerk transaction, and fixed Borrower to c...
Merge pull request #18 from g2-aj/branch_lin

Branch lin
Merge branch 'master' into branch_lin
Finished Librarian transaction