clamav 0.98.5

* Version bump. 
* Fixed head.
* New recommend dependency *(It’s actually an old recommended dependency that we haven’t been building).* 
* Moves the sysconf dir to a directory inside HOMEBREW_PREFIX/etc to make it a little tidier.
* Adds some caveats to explain clamav’s confusing error messages on initial run.
* Adds a test.
Not easily; They're pretty lengthy files, but if desired I can ``` rm ``` them post-install and put functional defaults in place. Can either write those functional defaults into the formula (not really feasible, it'd be around 1000 lines of code) or curl an example in from somewhere (which may be potentially questionable given the nature of ``` clamav ```). Apple is probably our best bet if we wanted to go down the second route, as they have some default [clam settings](https://www.opensource.apple.com/source/SpamAssassin/SpamAssassin-124/Extra/etc/clamav.conf) available, but I'm not sure how well that link would work given the dodgy SSL/TLS cert it sits upon.

Clam themselves pretty much just say *Users should tweak their .conf files as necessary* :disappointed: