Various pep8 edits and course folder

Author: domokane

book/ALL FINANCEPY/products/bonds/FINBONDOPTION_HW_EXAMPLE_MATCH_DERIVA_GEN.ipynb

@@ -126,8 +126,8 @@
    },
    "outputs": [],
    "source": [
-    "df_times = discount_curve._times\n",
-    "df_values = discount_curve._dfs"
+    "df_times = discount_curve.times()\n",
+    "df_values = discount_curve.dfs()"
    ]
   },
   {

book/ALL FINANCEPY/products/bonds/FINBOND_ComparisonWithQLExample.ipynb

@@ -221,7 +221,7 @@
     }
    ],
    "source": [
-    "discount_curve._dfs"
+    "discount_curve.dfs()"
    ]
   },
   {

book/BLOOMBERG/pds-fx-forward.pdf

@@ -201,7 +201,7 @@
     }
    ],
    "source": [
-    "discount_curve._times"
+    "discount_curve.times()"
    ]
   },
   {
@@ -221,7 +221,7 @@
     }
    ],
    "source": [
-    "discount_curve._dfs"
+    "discount_curve.dfs()"
    ]
   },
   {