WIP: Wrap fastscapelib-fortran as processes and models

[benbovy]

Feature parity with fastscapelib-fortran

• [x] vertical uplift
• [x] single flow routing
• [x] multiple flow routing
• [x] adaptive multiple flow routing
• [x] flow accumulation
• [x] drainage area
• [x] diffusion
• [x] differential diffusion (kd vs kdsed)
• [x] SPL
• [x] differential SPL (kf vs kfsed)
• [x] extended SPL
• [x] differential extended SPL (g vs gsed)
• [x] terrain derivatives (slope, curvature)
• [x] rock advection
• [x] flexure
• [x] strati
• [x] marine
• [x] fluxes

Additional components

• [x] local isostasy
• [x] initial surfaces
  • [x] flat topography
  • [x] escarpment topography
  • [x] bare-rock surface
• [x] initial rates
  • [x] no erosion history
  • [x] escarpment differential uplift

Models:

• [x] basic model
• [x] bedrock / sediment model with differential erosion and channel incision, transport and deposition
• [x] marine model