Documentation: fix multiple errors and warnings

Multiple files were badly formatted, which resulted in many
warnings. This made it harder to check for errors in newly
written documentation.

What's worse, badly formatted text resulted in butchered
output in generated html.

This patch fixes most of the errors, but alas, not all of
the errors can be fixed. Anyway, this should be way easier
to spot errors in newly written docs now.

Signed-off-by: Michał Łyszczek <michal.lyszczek@bofc.pl>

Documentation/reference/os/arch.rst

@@ -123,21 +123,21 @@ APIs Exported by Architecture-Specific Logic to NuttX
   -  ``stack_base_ptr``: Adjusted stack base pointer after the TLS Data
      and Arguments has been removed from the stack allocation.
 
-  Here is the diagram after some allocation(tls, arg):
+  Here is the diagram after some allocation(tls, arg)::
 
-                   +-------------+ <-stack_alloc_ptr(lowest)
-                   |  TLS Data   |
-                   +-------------+
-                   |  Arguments  |
-  stack_base_ptr-> +-------------+\
-                   |  Available  | +
-                   |    Stack    | |
-                |  |             | |
-                |  |             | +->adj_stack_size
-                v  |             | |
-                   |             | |
-                   |             | +
-                   +-------------+/
+                     +-------------+ <-stack_alloc_ptr(lowest)
+                     |  TLS Data   |
+                     +-------------+
+                     |  Arguments  |
+    stack_base_ptr-> +-------------+\
+                     |  Available  | +
+                     |    Stack    | |
+                  |  |             | |
+                  |  |             | +->adj_stack_size
+                  v  |             | |
+                     |             | |
+                     |             | +
+                     +-------------+/
 
   :param tcb: The TCB of new task.
   :param frame_size: The size of the stack frame to allocate.

Documentation/reference/user/02_task_scheduling.rst

@@ -55,7 +55,7 @@ Functions
   name. Differences from the full POSIX implementation include:
 
     -  The range of priority values for the POSIX call is 0 to 255. The
-      priority 0 is the lowest priority and 255 is the highest priority.
+       priority 0 is the lowest priority and 255 is the highest priority.
 
   .. note:: Setting a task's priority to the same value has the similar effect
     to ``sched_yield()``: The task will be moved to after all other tasks

Documentation/reference/user/13_boardctl.rst

@@ -184,7 +184,7 @@ USB
    
    :configuration: CONFIG_BOARDCTL && CONFIG_BOARDCTL_USBDEVCTRL
    
-   :dependencies: Board logic must provide ``board_<usbdev>_initialize()`.
+   :dependencies: Board logic must provide `board_<usbdev>_initialize()`.
    
 Graphics
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