Add commandline cache inspection tools

[Martin Sandve Alnæs]

Examples that could be useful:

• dijitso status show size etc.

• dijitso clean clean entire cache

• dijitso extract <hash> copy src or lib files from cache to current directory

• dijitso gc delete least used modules to make size bounded

• dijitso config foolproof interface to config file

• dijitso src-grep <pattern> grep in all source files

• dijitso lib-grep <pattern> grep in library file symbols

Implement on demand.

[Martin Sandve Alnæs]

dijitso-cache script now in next, more features can always be added but enough for now.