rpn/Changelog.md

Changelog

- Better parser (now called lexer)
- Use of mpreal instead of raw mpfr for calc on reals
- Use of C++ complex class
- Removing old memory management, efficient but poorly maintainable
- Enhanced code quality and memory usage checks
- Added CircleCI checks: passing functional tests and valgrind mem checks at each pull request
- SonarCloud integration, Sonar way profile
- clang-format now based on google style
- [google c++ style guide](https://google.github.io/styleguide/cppguide.html) applied
  - c++17
  - define guard
  - name and order of inclusions
  - static and global variables
    - common patterns (ex: no static maps or vectors)
  - classes (explicit)
  - naming:
    - file names (.cc .h), types (PascalCase), variables (snake_case), members (trailing _), static const (camelCase begining with k), enum (enum class, values like static const
    - consistent comments (//), class comments, functions comments
  - cpplint used with a CPPLINT.cfg removing some warnings
- Test files are now markdown (.md) files, tests result are slightly changed
- Delivery as flatpak and snap
- error string are slightly different, althought error codes are still the same

New
- `«` and `»` are now valid as program delimiters. `<<` and `>>` are still valid
- entering the sign after the base (ex: 0x-1e2) is allowed
- rpn is delivered as flatpak and snap packages to be compatible with a maximum of Linux distribs. rpm and deb are no longer generated

Compatibility is broken on these points
- `<< <<` input doesn't lead to `««»»` but to `«<< »`, preventing to eval the real program content
- `1 2+` not allowed anymore, keep `1 2 +`, this corrects bad behaviors like `3b114` pushing `3b11` and `4`
- complexes are written in the form `(1,2)` instead of `(1, 2)` (space is removed)
- removed useless `unti`, `repea`, `whil` (prev.existing for HP28S compatibility)
- removed `sqr` function, please use `sq` instead (prev.existing for HP28S compatibility)
- the binary prefix is always 0b on display, but still can be 0b, 0B, 2b or 2B at input
- the hex prefix is always 0x on display, but still can be 0x, 0X or 16B at input
- `mant` and `xpon` now give binary (and not decimal) significand and exponent, as it is the norm in standard libs (libC, standard C++, mpfr, gmp)
- `dupn`, `roll`, `rolld` are not leaving anymore their argument in front of the stack in case of error
- `sto+` `sto-` `sto*` `sto/` don't accept anymore the syntax `'varname' value stoX`, but only `value 'varname' stoX`, ex: `3 'a' sto*`
- incomplete entry `(1,` is not available anymore
- signed zero is the sign of zero is subject to change  compared to previous version, for example `-3 sqrt` now equals `(0.000000,1.732051)` instead of `(-0.000000,1.732051)`
- removed CtrlC for interrupting a program (considered useless)

Debug 
- `sub` now only accepts boundaries between 1 and the string length
- `sto/` behavior: sto/ now correctly stores variable / constant and not constant / variable
- `cosh` now returns the hyp cosinus instead of the hyp sinus (!)