Adds some docstring to pybind function and some refactors

Author: StephenNneji

MANIFEST.in

@@ -1,5 +1,5 @@
-include README.md
-recursive-include cpp/RAT *
+include README.md 
+recursive-include cpp *
 prune tests
 prune */__pycache__ 
 global-exclude .git

RATapi/examples/normal_reflectivity/background_function.py

@@ -1,7 +1,7 @@
 import numpy as np
 
 
-def backgroundFunction(xdata, params):
+def background_function(xdata, params):
     # Split up the params array
     Ao = params[0]
     k = params[1]

RATapi/utils/plotting.py

@@ -158,8 +158,7 @@ def plot_ref_sld_helper(
                     layers[-1, 1],  # Bulk Out
                     data.subRoughs[i],  # roughness
                     layer,
-                    len(layer),
-                    1.0,
+                    1,
                 )
 
                 sld_plot.plot(