Bugfixes.

This PR: 
- Fixes #161
- Fixes #152
- Fixes #148
- Fixes #105
- Fixes #94

cc @whatsdis, @clarkewd, @sjongejan, @mar-chi-pan, @bartvw

Feel free to check out this branch and run slanger by invoking `bin/slanger` from the project root. Let me know if you have issues.

This will be one of the last PRs to this codebase, a complete rewrite is nearly ready with many new requested features.

:christmas_tree: :santa: :heart: