Borer fixes

```yaml
changes:
- rscadd: "Borers receive a brief instructional greeting and receive objectives."
- bugfix: "Borers and host brains can communicate properly now."
- bugfix: "Borer chat is propagated to ghosts and fellow borers properly."
- bugfix: "Borer chat is stripped of the beginning ;."
- bugfix: "Standardized borer vent-crawling, now uses same system as other vent-crawling mobs."
```
Also fixes exploit where borer that takes control of a corpse can see ghostchat.