Fixed #417: rendering applet file tags from readmes

The readme sanitization code was effectively a no-op because of a code sequencing error. elevateLatestVersionInfo() was being called *after* readme sanitization and replacing all the cleaned data with unsanitized original content. Because it wasn't being called, the markdown & sanitization process was likely always failing anyway.

Made several changes to improve code readability & clarity, as well as to fix the bug:

- Changed the name of `package()` to match how it's used: `presentPackage()`
- Moved `elevateLatestVersionInfo()` to much earlier in `presentPackage()`
- Changed `parseReadme()` to no longer require a callback, since it isn't actually async
- Restructured `parseReadme()` so that all paths through it, including the code path where marked parsing fails, return sanitized data. It no longer can return an error.
- Defended against null readme blocks being passed into `parseReadme()`.
- Fixed a problem in the package route where the `pkg` variable from a callback was shadowing an existing variable.

The package to use when testing this fix is `benchmark`, which has now been added to the list of common packages that a dev installation will replicate.