20230403.01

Cleanup Makefiles (#95)

- consistent formating across all files (space between a target and
  a semicolon)
- add targets for installing build dependencies on RHEL-like systems
  (this is useful for quick creation of a build/dev environment)
- the clean target now cleans a bit better
- installation of man-pages doesn't ask for confirmations on overrides
- clearly defined a default target