Release 0.5.1 "Talents": More RPL commands

This release focuses on rounding up various useful RPL commands and bringing RPL a bit closer to feature-complete.

New features:

• Portable bit pattern generation commands, gray and rgb (#617)
• Add support for packed bitmaps (#555)
• Implement RPL case statement, extended with case when (#374)
• Beep command (#50)
• List→ command (#573)
• Size command (#588)
• Str→ command (#590)
• Obj→ command (#596)
• Add flag to control if 0^0 returns 1 or undefined behaviour (#598)
• Unicode-based Num and Chr commands, Text→Code and Code→Text (#597)
• IP and FP commands (#601)
• Percentage operations %, %CH and %T (#602)
• Min and Max operations (#603)
• Floor and Ceil operations (#605)
• Get with a name argument (#609)
• Put command (#610)
• Head and Tail commands (#614)
• Map, Reduce and Filter commands (#613)

Bug fixes:

• Ensure rounded rectangles stay within their boundaries (#618)
• Prevent auto-power-off for long-running programs (#587)
• Fix old-style RPL shortcuts for FS?C and the like
• Add FF shortcut for FlipFlag
• Fix rendering of <, >, etc in old-style RPL compatibility mode (#595)
• Update various menus
• Evaluate program arguments in IFT and IFTE (#592)
• Evaluate algebraic expressions in if, while and case (#593)
• Load variables from state file in correct order (#591)
• Avoid truncation of state file when ASCII conversions occur (#589)
• Clear debugging state more completely after kill (#600)
• Wait no longer makes it harder to stop a program (#619)
• mod no longer gives wrong result for negative fractions and bignums (#606)
• No longer strip tags in non-numeric arithmetic operations (#607)

Improvements:

• Small updates to demo file
• A long Wait command allows the calculator to switch off (#620)
• Centering of variable names in VariablesMenu (#610)
• Makefile check-ids target to check if commands are in help or menus (#615)

Full Changelog: v0.5.0...v0.5.1