Use backtick to simplify `with-package-test'
Merge `with-package-x-test' into `with-package-test'

They were mostly identical, so they can be consolidated.
Rename `package-buffer-info' to `package-desc-from-buffer'

It is more descriptive of what it does.
Follow convention for indication of private symbols.

Symbols which are intended to be private to a package should be named like
"foo--func" instead of "foo-func" to indicate that the symbol is not meant for
use outside of the package itself.