pressure bounds derivations

1. pressure ranges from midpoints

   symbol	description	unit	variable name
   \(p(i)\)	pressure	\(Pa\)	pressure {:,vertical}
   \(p^{B}(i,l)\)	pressure boundaries (\(l \in \{1,2\}\))	\(Pa\)	pressure_bounds {:,vertical,2}

   The pattern : for the dimensions can represent {time}, or no dimension at all.

   \begin{eqnarray} p^{B}(1,1) & = & e^{2\ln(p(1)) - \ln(p(2))} \\ p^{B}(i,1) & = & e^{\frac{\ln(p(i-1)) + \ln(p(i))}{2}}, 1 < i \leq N \\ p^{B}(i,2) & = & e^{\ln(p^{B}(i+1,1))}, 1 \leq i < N \\ p^{B}(N,2) & = & e^{2\ln(p(N)) - \ln(p(N-1))} \end{eqnarray}

   This formula applies if the harp option regrid_out_of_bounds is set to nan or to extrapolate. If the option is set to edge then the first and last boundary value are set to the midpoints (\(p^{B}(1,1) = p(1)\), \(p^{B}(N,2) = p(N)\)).