ensure that % is escaped during percent encoding

[jcreekmore]

Since the % sign is used for the escape in percent encoding, we need to ensure that that is itself escaped if found in the input. Debian git tags in vcs_urls in particular seem to be moving to replacing the : in a version like 1:41.1 into 1%41.1. The correct encoding of that winds up being 1%2541.1. Without this, adding the vcs_url as it is given will wind up forcing the parsing of the subsequent displayed PackageUrl to decode the 1%41.1 as 1A.1.

Fixes #12.

[codecov[bot]]

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[ctron]

Thanks for the PR. It's released as 0.4.1, which also has some compatibility for the 0.3.x version.

[jcreekmore]

Thanks!