Release 0.7.17 "Open" - DoSubs, DoList, entering units

This release adds DoSubs, DoList, NSub and EndSub commands, and fixes related issues that were found with the associated examples in the HP50G Advanced Reference Manual.

Features

• lists: Implement DoList, DoSubs, NSub and EndSub
• units: Add usual "big" units to Computing units menu (e.g. KB, MB)
• graphics: Add Freeze command
• ui: Make it easier to enter units
• expressions: Accept algebraic forms for integrate and root
• expressions: Graphical rendering of integrals

Bug fixes

• case: Preserve the code for the default case (which was lost before)
• parser: Parse arg-less alegbraic commmands such as NSub
• equations: Fix syntax errors in built-in equations, e.g. missing parentheses
• equations: Replace variables that match DB48X command names, e.g. Re
• equations: Replace imperial units with SI units, e.g. in with cm
• units: Reject user-defined functions in unit expressions
• constants: Fix definition for the qε0 constant

Improvements

• Update help about equations with some additional material
• tests: Run through all the builtin equations
• ui: Do not insert an extra space before parentheses in equation
• simulator: Add macOS icons for DB48X and DB50X
• font: Record saved font with v update

Full Changelog: v0.7.16...v0.7.17