bpo-15817: Expose command documentation to gdb help (GH-6384)

Original patch by Alexander Belopolsky.  Patch by Skip Montanaro.

Misc/gdbinit

@@ -14,9 +14,11 @@
 # with embedded macros that you may find superior to what is in here.
 # See Tools/gdb/libpython.py and http://bugs.python.org/issue8032.
 
-# Prints a representation of the object to stderr, along with the
-# number of reference counts it current has and the hex address the
-# object is allocated at.  The argument must be a PyObject*
+document pyo
+  Prints a representation of the object to stderr, along with the
+  number of reference counts it currently has and the hex address the
+  object is allocated at.  The argument must be a PyObject*
+end
 define pyo
     # side effect of calling _PyObject_Dump is to dump the object's
     # info - assigning just prevents gdb from printing the
@@ -24,14 +26,18 @@ define pyo
     set $_unused_void = _PyObject_Dump($arg0)
 end
 
-# Prints a representation of the object to stderr, along with the
-# number of reference counts it current has and the hex address the
-# object is allocated at.  The argument must be a PyGC_Head*
+document pyg
+  Prints a representation of the object to stderr, along with the
+  number of reference counts it currently has and the hex address the
+  object is allocated at.  The argument must be a PyGC_Head*
+end
 define pyg
     print _PyGC_Dump($arg0)
 end
 
-# print the local variables of the current frame
+document pylocals
+  Print the local variables of the current frame.
+end
 define pylocals
     set $_i = 0
     while $_i < f->f_code->co_nlocals
@@ -69,7 +75,9 @@ define lineno
     printf "%d", $__li
 end
 
-# print the current frame - verbose
+document pyframev
+  Print the current frame - verbose
+end
 define pyframev
     pyframe
     pylocals
@@ -126,7 +134,9 @@ end
 # the interpreter you may will have to change the functions you compare with
 # $pc.
 
-# print the entire Python call stack
+document pystack
+  Print the entire Python call stack
+end
 define pystack
     while $pc < Py_Main || $pc > Py_GetArgcArgv
         if $pc > PyEval_EvalFrameEx && $pc < PyEval_EvalCodeEx
@@ -137,7 +147,9 @@ define pystack
     select-frame 0
 end
 
-# print the entire Python call stack - verbose mode
+document pystackv
+  Print the entire Python call stack - verbose mode
+end
 define pystackv
     while $pc < Py_Main || $pc > Py_GetArgcArgv
         if $pc > PyEval_EvalFrameEx && $pc < PyEval_EvalCodeEx
@@ -148,7 +160,9 @@ define pystackv
     select-frame 0
 end
 
-# generally useful macro to print a Unicode string
+document pu
+  Generally useful macro to print a Unicode string
+end
 def pu
   set $uni = $arg0
   set $i = 0