epics formula added

The problem is actually that it's installing a *directory* here. `/usr/local/bin` shouldn't have any subdirectories; if a project is going to install binaries, they should go directly into `bin`.

An alternative option might be to install the entirety of EPICS into somewhere outside the publicly-linked Homebrew prefix, and symlink in the parts of the software that do respect a standard prefix (if that's needed). For example, you could install it to `libexec` instead of `prefix`.