Testing suite roadmap

There has been great progress in building up the test part of the test suite, however the software running the tests is quite lacking.
A replacement should be developed that fulfills the following criteria.
- [x] imports src/main.nim instead of running pre-built binaries
- [x] Runs tests parallel (multiple instances of japl)
- [x] Separates stdout/stderr output

With this, a more advanced testing language is needed.
- [x] Replace output: with stdout: stderr: (and stdin:)
- [x] Allow for multiple tests per file
- [x] Allow regex (or peg) matches (handy for exception messages)

The visual of the test runner also needs improvement:
- [x] Add a progress bar indicating test progress
- [x] Improve the CLI (flags for verbosity and such)

Long term improvements:
- [ ] Allow writing a parallel test in python (checks if output matches)
- [ ] Benchmark support

Start by reading src/main.nim and reviewing the testing-suite roadmap, including the completed runner requirements and the remaining Python parallel-test and benchmark items. Done would require a defined implementation scope for those long-term improvements, but the issue does not identify runner files or tests to run.

Written by the indexing model from the issue text.