PurlDB: Collect core package metadata (including generic packages)

[DennisClark]

Add support for Collecting core metadata for PURLs present in #326 #327 #328 and #329

[keshav-space]

Completed in these issues and PRs:

• Add support for directory listed source archives in package.info fetchcode#107
• purl2sym: Add metadata support for packages hosted on GitHub fetchcode#112
• purl2sym: Add metadata support for linux, mtd-utils, barebox, e2fsprogs and erofs-utils fetchcode#113
• Add metadata support for openssl, udhcp fetchcode#114
• Use authenticated requests for GitHub REST API calls fetchcode#115

To test this, to follow the below steps:

1. Install fetchcode using pip install fetchcode
2. Call the fetchcode.package.info using PURL

Example:

>>> from fetchcode.package import info
>>> packages = list(info("pkg:generic/ipkg@0.99.19"))
>>> packages[0]
OrderedDict([('type', 'generic'), ('namespace', None), ('name', 'ipkg'), ('version', '0.99.19'), ('qualifiers', OrderedDict()), ('subpath', None), ('primary_language', None), ('description', None), ('release_date', '2002-08-19T04:23:00'), ('parties', []), ('keywords', []), ('homepage_url', 'https://web.archive.org/web/20090326020239/http://handhelds.org/download/packages/ipkg/'), ('download_url', 'https://web.archive.org/web/20090326020239/http:/handhelds.org/download/packages/ipkg/ipkg_0.99.19_arm.ipk'), ('api_url', None), ('size', None), ('sha1', None), ('md5', None), ('sha256', None), ('sha512', None), ('bug_tracking_url', None), ('code_view_url', None), ('vcs_url', None), ('copyright', None), ('license_expression', None), ('declared_license', None), ('notice_text', None), ('root_path', None), ('dependencies', []), ('contains_source_code', None), ('source_packages', []), ('purl', 'pkg:generic/ipkg@0.99.19'), ('repository_homepage_url', None), ('repository_download_url', None), ('api_data_url', None)])