API revisions

[bmorris3]

• switching to pymc3-style sampling in docs, deleting the sample_nuts, sample_smc, optimize methods.
  • new plan is to use pm.sample, pm.smc.sample_smc and pm.find_MAP methods
• adding a forward model tutorial
• switching to partition_lons=True by default
• letting stellar inclination vary all the way from (0, pi/2)