For ELF binaries (e.g., Linux): default compatible version (SONAME =
`<library-name>.so.<MAJOR>`) can be specialized using additional `cnum`
parameter to `<library-name>.so.<MAJOR>.<MINOR>` or
`<library-name>.so.<MAJOR>.<MINOR>.<PATCH>`.

For Mach-O binaries (e.g., OS X):

- (bugfix) install-name points to compatible version (not absolute path
  to a non-versioned library)
- Default install-name `<install-path>/<library-name>.<MAJOR>.dylib` can
  be specialized using `cnum` parameter to
  `<install-path>/<library-name>.<MAJOR>.<MINOR>.dylib` or
  `<install-path>/<library-name>.<MAJOR>.<MINOR>.<PATCH>.dylib`
- `-Wl,-compatibility_version` and `-Wl,-current_version` flags use
  version from cnum/vnum (default cnum is vnum.split('.')[0])