Feature: purl2sym: Collecting and indexing symbols

[pombredanne]

This feature is about collecting the core package metadata along with symbols from source code and storing these symbols in the PurlDB and further indexing these to later support querying. This includes updating PurlDB to add REST API endpoints that respond to PURLs, and creating ScanCode.io pipelines to collect and store symbols in a scan.

• PurlDB: Collect core package metadata (including generic packages) #321
• ScanCode.io: Collect symbols in scan (from source code and store in scan results) scancode.io#1106
• PurlDB: Store symbols (from scan results) in the PurlDB #323
• PurlDB: Collect package symbols (API endpoint using PURL input, download then collect and store symbols) #324
• PurlDB: Collect symbols for arbitrary download URL (API endpoint either as a free standing API or creating a generic or inferred PURL) #325

[pombredanne]

This is completed. For testing, PR and other details see:

• PurlDB: Collect core package metadata (including generic packages) #321 (comment)
• ScanCode.io: Collect symbols in scan (from source code and store in scan results) scancode.io#1106 (comment)
• PurlDB: Store symbols (from scan results) in the PurlDB #323 (comment)
• PurlDB: Collect package symbols (API endpoint using PURL input, download then collect and store symbols) #324 (comment)
• PurlDB: Collect symbols for arbitrary download URL (API endpoint either as a free standing API or creating a generic or inferred PURL) #325 (comment)