Provide header level details for a scan: Enhance scancode to include a log or history with useful statistics

[DennisClark]

A run of scancode should generate a log file with meaningful statistics, including such things as:

• the version number of scancode that was executed
• start date/time
• end date/time
• elapsed time
• name of the library that was scanned
• number of files scanned
• {{anything else that makes sense and is useful}}

[balusarakesh]

This log file can also contain the reason for the scan failure if the scan is interrupted in the middle due to any particular reasons.

[pombredanne]

See also aboutcode-org/aboutcode#7