[apc_status] Added multigraph capabilities and fixed regex

Added mutigraph capabilities and automatic unit detection.

Fixed regex:
`egrep "$key"` was returning multiple matches when using "BATTV" as key.
Fixed by using `egrep "^$key"`.
This prevents the key `NOMBATTV` from being matched by the string `BATTV` while still allowing it to be matched by `NOMBATTV`