add is_pkgname_similar

[anandijain]

i refactored a bit to make it easier to check if your package name is too similar to existing package names

i think tests rely on having the uncompressed General, so I don't know if tests pass yet.

the reason I wanted this is so I could build a pkg_search function that lets me search for packages from the repl

very sorry for juliaformatter

[ericphanson]

can you undo the unrelated formatting changes? it makes it harder to review