design: gstpipeline: fix missing markup

Fix a few other minor issues too.

markdown/design/gstpipeline.md

@@ -5,7 +5,7 @@ with a clock.
 
 A `GstPipeline` also provides a toplevel `GstBus` (see [gstbus](design/gstbus.md))
 
-The pipeline also calculates the running\_time based on the selected
+The pipeline also calculates the `running_time` based on the selected
 clock (see also clocks.txt and [synchronisation](design/synchronisation.md)).
 
 The pipeline will calculate a global latency for the elements in the
@@ -17,31 +17,31 @@ In addition to the normal state change procedure of its parent class
 `GstBin`, the pipeline performs the following actions during a state
 change:
 
-- NULL → READY:
+- `NULL` → `READY`:
   - set the bus to non-flushing
-- READY → PAUSED:
-  - reset the running_time to 0
-- PAUSED → PLAYING:
-  - Select and a clock.
-  - calculate base_time using the running_time.
+- `READY` → `PAUSED`:
+  - reset the `running_time` to 0
+- `PAUSED` → `PLAYING`:
+  - Select a clock.
+  - calculate `base_time` using the `running_time`.
   - calculate and distribute latency.
-  - set clock and base_time on all elements before performing the state
+  - set clock and `base_time` on all elements before performing the state
     change.
-- PLAYING → PAUSED:
-  - calculate the running_time when the pipeline was PAUSED.
-- READY → NULL:
+- `PLAYING` → `PAUSED`:
+  - calculate the `running_time` when the pipeline was `PAUSED`.
+- `READY` → `NULL`:
   - set the bus to flushing (when auto-flushing is enabled)
 
-The running_time represents the total elapsed time, measured in clock
+The `running_time` represents the total elapsed time, measured in clock
 units, that the pipeline spent in the PLAYING state (see
-[synchronisation](design/synchronisation.md)). The running_time is set to 0 after a
+[synchronisation](design/synchronisation.md)). The `running_time` is set to 0 after a
 flushing seek.
 
 ## Clock selection
 
 Since all of the children of a `GstPipeline` must use the same clock, the
 pipeline must select one. This clock selection happens when the
-pipeline goes to the PLAYING state.
+pipeline goes to the `PLAYING` state.
 
 The default clock selection algorithm works as follows:
 
@@ -50,14 +50,14 @@ The default clock selection algorithm works as follows:
 - Use the clock of the most upstream element that can provide one.
 This selection is performed by iterating the element starting from
 the sinks going upstream.
-  - since this selection procedure happens in the PAUSED→PLAYING
+  - since this selection procedure happens in the `PAUSED` → `PLAYING`
     state change, all the sinks are prerolled and we can thus be
     sure that each sink is linked to some upstream element.
   - in the case of a live pipeline (`NO_PREROLL`), the sink will not
     yet be prerolled and the selection process will select the clock
     of a more upstream element.
 
-- use `GstSystemClock`, this only happens when no element provides a
+- Use `GstSystemClock`, this only happens when no element provides a
 usable clock.
 
 The application can influence this clock selection with two methods: