nimble url-dependency is dependent on package-name only
In best case a url dependency like `requires "https://github.com/user/package >= 1.2.3"` should require the package from the given url, in the given version. That means the package should be detected by package name + package version + package author (+ maybe package url).
Currently my tests with different package names and different versions show that it only depends on package name + package version. That means package name `A` from source `S2` in version `V2` is considered an update of `A` from source `S1` with version `V1` if `V2` > `V1`. This is normally not the case if `V1.repoUrl != V2.repoUrl` and will cause hard problems.
A package with same name from different author will break code dependent on this import (See https://github.com/nim-lang/nimble/issues/573 that it will break existing code).

Example:
1) `nimble install https://github.com/ephja/lzma` install `lzma @ 0.1.0`; `import lzma` does work.
2) `nimble install https://github.com/tim-st/nim-zim@#nimble-same-name`
Installs `lzma @ 0.1.1` and `zim @ 0.1.0`:
```
C:\Users\->nimble install https://github.com/tim-st/nim-zim@#nimble-same-name
Downloading https://github.com/tim-st/nim-zim using git
  Verifying dependencies for zim@#nimble-same-name
      Info: Dependency on cligen@>= 0.9.16 already satisfied
  Verifying dependencies for cligen@#head
 Installing https://github.com/tim-st/nim-lzma@#test-nimble-version
Downloading https://github.com/tim-st/nim-lzma using git
  Verifying dependencies for lzma@#test-nimble-version
 Installing lzma@#test-nimble-version
   Success: lzma installed successfully.
 Installing zim@#nimble-same-name
   Success: zim installed successfully.
```
And consideres it working.
Now import `lzma` doesnt work anymore.
`import zim` doesnt work too, because it depends on `lzma`.