Cleaner bill page, smarter rate formulas, ledger on bill

In this update

• BetterThe Bill screen now reads like a clean page; printed bills and PDFs look as before
• NewRate formulas get IF, < > and SLAB keys, with a Help guide
• NewTwo new ready-made formulas: Fat or Fat+SNF, and SNF Slab
• NewOpen the client's ledger straight from the Bill screen
• NewEdit or delete a transaction right from Transaction History
• BetterBill History: search the client by name, in a cleaner card look
• BetterStability and speed improvements