replace all usages of `exit` ...

- those skipped the ERR trap
- add die function to exit with line number and message

unify flags and error handling ...

- also add trap ERR handler to report exact error location

silence confusing test output ...

- failure is expected and should not appear in logs as it's easily
  confused to be the cause for a failed test

split remove into callback- and version-selection overload ...

- make remove w/ --version non-interactive

use 1 based index for selection ...

- format similar to bash's select

interactive package removal ...

- ask user which version of a package to remove