Fix some sphinx errors

wrappers/python/simtk/openmm/app/charmmpsffile.py

@@ -117,6 +117,7 @@ class CharmmPsfFile(object):
 
     This structure has numerous attributes that are lists of the elements of
     this structure, including atoms, bonds, torsions, etc. The attributes are
+
     - residue_list
     - atom_list
     - bond_list
@@ -713,7 +714,7 @@ class CharmmPsfFile(object):
             solvent.
         implicitSolventSaltConc : float=0.0*u.moles/u.liter
             Salt concentration for GB simulations. Converted to Debye length
-            `kappa'
+            ``kappa``
         temperature : float=298.15*u.kelvin
             Temperature used in the salt concentration-to-kappa conversion for
             GB salt concentration term

wrappers/python/simtk/openmm/app/forcefield.py

@@ -445,16 +445,18 @@ class ForceField(object):
         generator : function
             A function that will be called when a residue is encountered that does not match an existing forcefield template.
 
-        When a residue without a template is encountered, the `generator` function is called with:
+        When a residue without a template is encountered, the ``generator`` function is called with:
 
         ::
            success = generator(forcefield, residue)
-        ```
 
-        where `forcefield` is the calling `ForceField` object and `residue` is a simtk.openmm.app.topology.Residue object.
+        where ``forcefield`` is the calling ``ForceField`` object and ``residue`` is a simtk.openmm.app.topology.Residue object.
+
+        ``generator`` must conform to the following API:
 
-        `generator` must conform to the following API:
         ::
+           generator API
+
            Parameters
            ----------
            forcefield : simtk.openmm.app.ForceField