Allow depends, pre-depends, recommends, and suggests to be arrays

[swlynch99]

This commit makes it so that depends (and any of the other fields above) can be written as

depends = ["a", "b", "c"]

in addition to the existing depends = "a, b, c" format.

It is converted at the config level by joining all the array elements with ", ". No additional validation is performed beyond that already done by serde deserialization.

I have tested this with a local crate and it appears to work as expected.

Closes #88

[kornelski]

Thanks