Clean up and move various subroutines.

- Fix indentation of get_compiler_info and clean up slightly.
- Move module_installed to make::utilities.
- Rename clean to cmd_clean and rewrite.
- Rename getcache to read_configure_cache and rewrite.
- Rename getrevision to get_revision.
- Rename makecache to write_configure_cache and rewrite.
- Rename showhelp to cmd_help and rewrite.
- Rename update to cmd_update and rewrite.
- Replace getmodules with a <src/modules/m_*.cpp> glob.