getting rid of phreatictop=True

[mbakker7]

To simulate a phreatic to aquifer, the user has to specify topboundary="conf" and phreatictop=True. Wouldn't it make more sense to define a new option topboundary=phreatic, which will do that all and get rid of the phreatictop=True? Thoughts?

[MattBrst]

Yes, I would vote in favor for this.

[mbakker7]

Fixed by #88