Log Message:
Update to 0.64

Upstream changes:
0.64      2021-07-10 15:42:56 -0600
  - Remove dependency on FindBin and File::Which (gh#51)
  - Improve backend fallback; no longer require
    ebug_backend_perl be in the PATH (gh#49, gh#51)
  - Fix ebug_server and ebug_client documentation to
    use underscores (gh#50, gh#51)